Ci a ion: Clemen , B.; S uwe, M.A.
The His o y o mARC. Molecules 2023,
28, 4713. h ps://doi.o g/10.3390/
molecules28124713
Academic Edi o : Gianan onio
Ba is uzzi
Recei ed: 12 May 2023
Re ised: 8 June 2023
Accep ed: 10 June 2023
Published: 12 June 2023
Copy igh : © 2023 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
This a icle is an open access a icle
dis ibu ed unde he e ms and
condi ions o he C ea i e Commons
A ibu ion (CC BY) license (h ps://
c ea i ecommons.o g/licenses/by/
4.0/).
molecules
Re iew
The His o y o mARC
Be nd Clemen 1,*,† and Michel A. S uwe 1,2,†
1
Pha mazeu isches Ins i u , Ch is ian-Alb ech s-Uni e si ä zu Kiel, Gu enbe gs aße 76, 24118 Kiel, Ge many;
[email p o ec ed]
2Zoologisches Ins i u —S uk u biologie, Zen um ü Biochemie und Molekula biologie,
Ch is ian-Alb ech s-Uni e si ä zu Kiel, Am Bo anischen Ga en 1−9, 24118 Kiel, Ge many
*Co espondence: [email p o ec ed]; Tel.: +49-431-880-4167
† These au ho s con ibu ed equally o his wo k.
Abs ac :
The mi ochond ial amidoxime- educing componen (mARC) is he mos ecen ly disco -
e ed molybdoenzyme in humans a e sul i e oxidase, xan hine oxidase and aldehyde oxidase. He e,
he imeline o mARC’s disco e y is b ie ly desc ibed. The s o y begins wi h in es iga ions in o
N-oxida ion o pha maceu ical d ugs and model compounds. Many compounds a e N-oxidized
ex ensi ely
in i o
, bu i u ned ou ha a p e iously unknown enzyme ca alyzes he e o educ ion
o he N-oxygena ed p oduc s
in i o
. A e many yea s, he molybdoenzyme mARC could inally be
isola ed and iden i ied in 2006. mARC is an impo an d ug-me abolizing enzyme and N- educ ion
by mARC has been exploi ed e y success ully o p od ug s a egies, ha allow o al adminis a ion
o o he wise poo ly bioa ailable he apeu ic d ugs. Recen ly, i was demons a ed ha mARC is a key
ac o in lipid me abolism and likely in ol ed in he pa hogenesis o non-alcoholic a y li e disease
(NAFLD). The exac link be ween mARC and lipid me abolism is no ye ully unde s ood. Rega dless,
many now conside mARC a po en ial d ug a ge o he p e en ion o ea men o li e diseases.
This a icle ocusses on disco e ies ela ed o mammalian mARC enzymes. mARC homologues ha e
been s udied in algae, plan s and bac e ia. These will no be discussed ex ensi ely he e.
Keywo ds: mARC; molybdenum enzyme; bio ans o ma ion; educ ase; p od ug
1. F om N-Oxygena ion o N-Reduc ion
Acco ding o ou cu en knowledge, mARC enzymes ac as educ ases. Howe e ,
a he han wi h educ ion, his s o y begins wi h oxida ion. My ea ly esea ch ca ee was
ocused on s udying he me abolic bio ans o ma ion o pha maceu ical d ugs. Fo example,
du ing my pos doc phase a Chelsea College, London, I disco e ed he N-oxygena ion as a
no el bio ans o ma ion pa hway o p ome hazine in abbi li e [
1
]. Du ing my “habili a-
ion” in F eibu g, I was able o show ha benzamidine (BA) and se e al ing-subs i u ed
de i a i es can be oxidized o benzamidoxime (BAO) by abbi li e homogena es [
2
]. This
eac ion appea ed o be ca alyzed by P450 monooxygenases a he han la in-con aining
monooxygenase (FMO) [
3
,
4
], disp o ing he p e iously p oposed “pK
a
” concep o N-
oxida ion [
5
,
6
], acco ding o which nonbasic ni ogen compounds a e oxidized by P450
monooxygenases, whe eas basic ni ogen species a e oxidized by FMO. N-oxygena ion
owa ds he espec i e amidoxime e en akes place o N-subs i u ed BA de i a i es,
such as N- e -bu yl benzamidine [
7
] o N-phenyl benzamidine [
4
], whe eas in ce ain
N-subs i u ed BA de i a i es, N-oxygena ion can lead o subsequen N-dealkyla ion [
8
].
My g oup conduc ed u he in es iga ions in o he oxida ion o benzamidoxime and i s
de i a i es by cy och ome P450 monooxygenases, ying o ind s uc u e–ac i i y ela-
ionships and mechanis ic insigh s [
9
]. Benzamidine and benzamidoxime ha e emained
impo an model compounds in my labo a o ies o he pas decades.
Despi e o he wise being simila o amidines, N-oxygena ion o guanidines was no ob-
se ed [
10
]. Howe e , many ela ed ni ogen unc ions such as N-N’-diphenylguanidines [
11
],
Molecules 2023,28, 4713. h ps://doi.o g/10.3390/molecules28124713 h ps://www.mdpi.com/jou nal/molecules
Molecules 2023,28, 4713 2 o 14
aminoguanidines [
12
] o he nucleobase adenine [
13
] could all be shown o unde go simila
N-oxygena ions as amidines. I was concluded ha N-oxygena ion by cy och ome P450
monooxygenases is possible o any ni ogen-con aining unc ional g oup wi hou
α
-H
a oms [14]. In he p esence o α-Ha oms, N-dealkyla ion is he compe ing eac ion [15].
Oxida ion o highly pola amidines such as BA by cy och ome P450 enzymes (Figu e 1)
was in ac a e y su p ising obse a ion a he ime. I had p e iously been belie ed ha
only hyd ophobic xenobio ics would unde go phase I bio ans o ma ion ( unc ionaliza-
ion) [
16
] in o de o inc ease hei hyd ophilici y and allow phase II bio ans o ma ion
(conjuga ion) [
17
], he biological pu pose being o acili a e exc e ion. Amidines and guani-
dines a e, howe e , al eady e y hyd ophilic, and conjuga ion is no necessa y o hei
elimina ion ia he kidney. Oxida ion o hese compounds dec eases hei hyd ophilici y
and migh he e o e necessi a e phase II bio ans o ma ion, despi e he pa en compounds
being highly soluble p io o phase I bio ans o ma ion. Indeed, we could show ha
p oduc s ob ained by N-oxygena ion o amidines a e subjec o addi ional Phase II bio ans-
o ma ion eac ions [18], he same being ue o N-hyd oxyla ed guanidines [19].
Molecules2023,28,xFORPEERREVIEW2o 15


Despi eo he wisebeingsimila  oamidines,N-oxygena iono guanidineswasno 
obse ed[10].Howe e ,many ela edni ogen unc ionssuchasN-N’-
diphenylguanidines[11],aminoguanidines[12]o  henucleobaseadenine[13]couldall
beshown ounde gosimila N-oxygena ionsasamidines.I wasconcluded ha N-
oxygena ionbycy och omeP450monooxygenasesispossible o anyni ogen-con aining
unc ionalg oupwi hou α-Ha oms[14].In hep esenceo α-Ha oms,N-dealkyla ionis
hecompe ing eac ion[15].
Oxida iono highlypola amidinessuchasBAbycy och omeP450enzymes(Figu e
1)wasin ac a e ysu p isingobse a iona  he ime.I hadp e iouslybeenbelie ed
ha onlyhyd ophobicxenobio icswouldunde gophaseIbio ans o ma ion
( unc ionaliza ion)[16]ino de  oinc ease hei hyd ophilici yandallowphaseII
bio ans o ma ion(conjuga ion)[17], hebiologicalpu posebeing o acili a eexc e ion.
Amidinesandguanidinesa e,howe e ,al eady e yhyd ophilic,andconjuga ionisno 
necessa y o  hei elimina ion ia hekidney.Oxida iono  hesecompoundsdec eases
hei hyd ophilici yandmigh  he e o enecessi a ephaseIIbio ans o ma ion,despi e
hepa en compoundsbeinghighlysolublep io  ophaseIbio ans o ma ion.Indeed,
wecouldshow ha p oduc sob ainedbyN-oxygena iono amidinesa esubjec  o
addi ionalPhaseIIbio ans o ma ion eac ions[18], hesamebeing ue o N-
hyd oxyla edguanidines[19].

Figu e1.Oxida ionando benzamidine(BA) obenzamidoximeand e o educ iono 
benzamidoxime obenzamidine.
While heN-oxygena iono BA oBAOwase iden enoughin i o,when issue
homogena esupe na an swe eused,Iwas,su p isinglyanda  he ime e y
disappoin ingly,no able oshow hisoxida ion ohappenin i o.The eason o  his
onlybecameob iousla e :whileBAcanbeoxidized oBAObycy och omeP450
monooxygenases, he ewasasecond eac ionhappening,speci ically, e o educ iono 
BAO oBA,whichisabsolu elydominan in i o.
A  he ime,i wascommon os udybio ans o ma ionwi hmic osomal ac ionso 
issuehomogena es.In abbi li e mic osomes(12,000×gsupe na an ),oxida iono BA
oBAOwasmuchmo ep onounced han he educ ion[20].On heo he hand,when
9000×gsupe na an so o he speciesa eused,conside able educ iono BAO oBAcan
bede ec ed[21].A  hesame ime,N- educ iono ano he benzamidoximede i a i ewas
epo ed[22].
A e pa en e aladminis a iono BA o a sand abbi s,only heglucu onide
conjuga eo BAO,bu no eeBAO,wasde ec edin heanimals’u ine,indica ing ha 
whileN-oxygena iondoesoccu , hep oduc isno me abolicallys able.Howe e ,when
BAOwasadminis e ed, he educedBAwasde ec edinhighconcen a ions,highligh ing
heimpo anceo N- educ ionin i o[23].
2.TheP od ugP inciple:AmidoximesIns eado Amidines
Thean ip o ozoalcompoundpen amidinewasanea lyexample o amedicinal
d ugcon aining woamidinemoie ies,whichcanunde goN-oxygena ion o o mei he 
amono-hyd oxyla edo abis-hyd oxyla edp oduc  h oughenzyma icN-oxygena ion.In
Figu e 1.
Oxida ion and o benzamidine (BA) o benzamidoxime and e o educ ion o benzami-
doxime o benzamidine.
While he N-oxygena ion o BA o BAO was e iden enough
in i o
, when issue ho-
mogena e supe na an s we e used, I was, su p isingly and a he ime e y disappoin ingly,
no able o show his oxida ion o happen
in i o
. The eason o his only became ob ious
la e : while BA can be oxidized o BAO by cy och ome P450 monooxygenases, he e was a
second eac ion happening, speci ically, e o educ ion o BAO o BA, which is absolu ely
dominan in i o.
A he ime, i was common o s udy bio ans o ma ion wi h mic osomal ac ions o
issue homogena es. In abbi li e mic osomes (12,000
×
gsupe na an ), oxida ion o BA
o BAO was much mo e p onounced han he educ ion [
20
]. On he o he hand, when
9000
×
gsupe na an s o o he species a e used, conside able educ ion o BAO o BA can
be de ec ed [
21
]. A he same ime, N- educ ion o ano he benzamidoxime de i a i e was
epo ed [22].
A e pa en e al adminis a ion o BA o a s and abbi s, only he glucu onide conju-
ga e o BAO, bu no ee BAO, was de ec ed in he animals’ u ine, indica ing ha while
N-oxygena ion does occu , he p oduc is no me abolically s able. Howe e , when BAO
was adminis e ed, he educed BA was de ec ed in high concen a ions, highligh ing he
impo ance o N- educ ion in i o [23].
2. The P od ug P inciple: Amidoximes Ins ead o Amidines
The an ip o ozoal compound pen amidine was an ea ly example o a medicinal d ug
con aining wo amidine moie ies, which can unde go N-oxygena ion o o m ei he a mono-
hyd oxyla ed o a bis-hyd oxyla ed p oduc h ough enzyma ic N-oxygena ion.
In i o
models using Plasmodium alcipa um o Leishmania mexicana showed hese N-hyd oxyla ed
pen amidine de i a i es o ha e p ac ically no an ip o ozoal ac i i y, co ela ing wi h a sig-
ni ican ly dec eased DNA binding [
24
]. In con as , ou g oup had p e iously syn hesized
bo h he mono-hyd oxyla ed and bis-hyd oxyla ed pen amidine de i a i es and s udied
hei an ip o ozoal ac i i y
in i o
, whe e bo h compounds we e ac i e [
25
]. These appa -
en ly con adic ing esul s can be explained by educ ion o he amidoxime compounds o
Molecules 2023,28, 4713 3 o 14
pen amidine
in i o
. Only he non-oxidized pen amidine is pha macologically ac i e, bu
hyd oxyla ed de i a i es a e ac i a ed by N- educ ion [26].
Rema kably, we de ec ed high pen amidine concen a ions in li e s, lungs and kidney
o a s a e o al adminis a ion o bis-hyd oxyla ed pen amidine, despi e he nonoxy-
gena ed pen amidine no being o ally bioa ailable [
26
], implying ha N-oxygena ion can
be used o inc ease o al bioa ailabili y o highly pola ni ogen-con aining compounds. As
was shown h ough
in i o
SPECT imaging o [
123
I]-labeled compounds, adminis a ion
o pen amidine p od ugs migh ha e ad an ages going beyond o al bioa ailabili y, e.g.,
highe concen a ions in he b ain o di e en elimina ion pa hways [27].
Amides a e s ongly basic (pKa
≈
10–12), and hus ca y a pe manen posi i e cha ge
in aqueous solu ion, which p ohibi s hei di usion ac oss biological memb anes. Ami-
doximes, on he o he hand, a e much less basic and can be abso bed in he gas oin es inal
ac . The educ ion o amidoximes o amidines can be exploi ed o o al adminis a-
ion o d ug subs ances con aining amidine moie ies: he co esponding amidoxime is
adminis e ed as a p od ug and apidly educed a e abso p ion in he gas oin es inal
ac [28].
Amidoxime p od ugs o e g ea lexibili y, as he amidoxime unc ional g oup can
be de i a ized u he o une physicochemical p ope ies (Figu e 2). In he case o he
model compound benzamidine, he N,N
0
-dihyd oxyamidine de i a i e was shown o ha e
an e en highe bioa ailabili y compa ed o he simple amidoxime [
29
]. Al e na i ely, he
amidoxime
−
OH g oup can be used o o m es e s wi h a ious ca boxylic acids such
as ace ic acid, succinic acid o e en amino acids such as aline. A e abso p ion, hese
es e s a e apidly hyd olyzed by es e ases, hus eleasing he amidoxime, which can be
educed o he ac i e amidine [
30
]. Also, he amidoxime migh be inco po a ed in o an
e he -like s uc u e, which is clea ed o he amidoxime by pep idylglycine
α
-amida ing
monooxygenase (PAM), which migh allow a ge ing o d ug subs ances o he cen al
ne ous sys em, whe e PAM exp ession le els a e highes [31].
Molecules2023,28,xFORPEERREVIEW3o 15
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
i omodelsusingPlasmodium alcipa umo Leishmaniamexicanashowed heseN-
hyd oxyla edpen amidinede i a i es oha ep ac icallynoan ip o ozoalac i i y,
co ela ingwi hasigni ican lydec easedDNAbinding[24].Incon as ,ou g ouphad
p e iouslysyn hesizedbo h hemono-hyd oxyla edandbis-hyd oxyla edpen amidine
de i a i esands udied hei an ip o ozoalac i i yin i o,whe ebo hcompoundswe e
ac i e[25].Theseappa en lycon adic ing esul scanbeexplainedby educ iono  he
amidoximecompounds open amidinein i o.Only henon-oxidizedpen amidineis
pha macologicallyac i e,bu hyd oxyla edde i a i esa eac i a edbyN- educ ion[26].
Rema kably,wede ec edhighpen amidineconcen a ionsinli e s,lungsand
kidneyo  a sa e o aladminis a iono bis-hyd oxyla edpen amidine,despi e he
nonoxygena edpen amidineno beingo allybioa ailable[26],implying ha N-
oxygena ioncanbeused oinc easeo albioa ailabili yo highlypola ni ogen-
con ainingcompounds.Aswasshown h oughin i oSPECTimagingo [
123
I]-labeled
compounds,adminis a iono pen amidinep od ugsmigh ha ead an agesgoing
beyondo albioa ailabili y,e.g.,highe concen a ionsin heb aino diffe en elimina ion
pa hways[27].
Amidesa es onglybasic(pKa≈10–12),and husca yape manen posi i echa ge
inaqueoussolu ion,whichp ohibi s hei diffusionac ossbiologicalmemb anes.
Amidoximes,on heo he hand,a emuchlessbasicandcanbeabso bedin he
gas oin es inal ac .The educ iono amidoximes oamidinescanbeexploi ed o o al
adminis a iono d ugsubs ancescon ainingamidinemoie ies: heco esponding
amidoximeisadminis e edasap od ugand apidly educeda e abso p ionin he
gas oin es inal ac [28].
Amidoximep od ugsoffe g ea  lexibili y,as heamidoxime unc ionalg oupcan
bede i a ized u he  o unephysicochemicalp ope ies(Figu e2).In hecaseo  he
modelcompoundbenzamidine, heN,N′-dihyd oxyamidinede i a i ewasshown o
ha eane enhighe bioa ailabili ycompa ed o hesimpleamidoxime[29].Al e na i ely,
heamidoxime−OHg oupcanbeused o o mes e swi h a iousca boxylicacidssuch
asace icacid,succinicacido e enaminoacidssuchas aline.A e abso p ion, hese
es e sa e apidlyhyd olyzedbyes e ases, hus eleasing heamidoxime,whichcanbe
educed o heac i eamidine[30].Also, heamidoximemigh beinco po a edin oan
e he -likes uc u e,whichisclea ed o heamidoximebypep idylglycineα-amida ing
monooxygenase(PAM),whichmigh allow a ge ingo d ugsubs ances o hecen al
ne oussys em,whe ePAMexp essionle elsa ehighes [31].

Figu e2.Examples o p od ug-basedamidoximes.
Manyno eld ugcandida escon ainingamidine unc ionalg oupswe ede eloped
in he1990saspo en ialan icoagulan s, o eplace i aminKinhibi o swa a inand
phenp ocoumon,whichhadso a been heonlyo allya ailablean icoagulan s.Vi amin
Figu e 2. Examples o p od ug-based amidoximes.
Many no el d ug candida es con aining amidine unc ional g oups we e de eloped
in he 1990s as po en ial an icoagulan s, o eplace i amin K inhibi o s wa a in and
phenp ocoumon, which had so a been he only o ally a ailable an icoagulan s. Vi amin
K inhibi o s a e e y di icul o manage in ou pa ien ca e, in e ac wi h o he d ugs o
e en oods and can ha e e y dange ous side e ec s [
32
]. Pha maceu ical companies ied
o de elop al e na i es, which would only inhibi selec ed s eps wi hin he coagula ion
cascade, such as ac o Xa, ac o IIa ( h ombin) o glycop o ein IIb/IIIa [33].
Many o hese d ug candida es we e de i a i es o BA [
34
]. Mos a ge s wi hin he
coagula ion cascade a e se ine p o eases, and BA was known as an inhibi o o se ine
p o eases o a long ime [
35
]. Benzamidine can bind in o a nega i ely cha ged pocke nex
o he ac i e si e o hese se ine p o eases, whe e i mimics an a ginine side chain o he
p o ease’s subs a e and o ms a sal b idge o a conse ed aspa a e esidue (see Figu e 3).
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Kinhibi o sa e e ydifficul  omanageinou pa ien ca e,in e ac wi ho he d ugso 
e en oodsandcanha e e ydange oussideeffec s[32].Pha maceu icalcompanies ied
ode elopal e na i es,whichwouldonlyinhibi selec eds epswi hin hecoagula ion
cascade,suchas ac o Xa, ac o IIa( h ombin)o glycop o einIIb/IIIa[33].
Manyo  hesed ugcandida eswe ede i a i eso BA[34].Mos  a ge swi hin he
coagula ioncascadea ese inep o eases,andBAwasknownasaninhibi o  o se ine
p o eases o along ime[35].Benzamidinecanbindin oanega i elycha gedpocke nex 
o heac i esi eo  hesese inep o eases,whe ei mimicsana gininesidechaino  he
p o ease’ssubs a eand o msasal b idge oaconse edaspa a e esidue(seeFigu e3).

Figu e3.Benzamidinebinds o h ombinby o mingasal b idgewi haspa a e189inp oximi y
o heca aly ic iadconsis ingo se ine195,his idine57andaspa a e102,ascanbeseenin he
c ys als uc u eo benzamidine-boundhuman h ombin(PDB:4UEH)[36].Panel(A):Ca oon
ep esen a ion.Panel(B):Elec os a icsu ace ep esen a ion.Theelec os a icpo en ialswe e
calcula edwi hAPBS[37]anda e ep esen edasacolo g adien  om ed—10k
B
T/e
c
o e whi e0
k
B
T/e
c
 oblue+10k
B
T/e
c
.
TheBAmoie yimi a ing heguanidine unc ionalg oupo a gininein hena u al
subs a e ib inogenis he e o es ic ly equi ed o  hepha macokine icp ope ieso 
heseno elan icoagulan d ugsandcanno be eplacedbyalesspola g oup.Howe e ,
he eeamidinesusuallylead opoo bioa ailabili y.Inmanycases, heamidoxime
p od ugp inciplecanbeappliedsuccess ully oinc ease heo albioa ailabili y,e.g., o 
heglycop o einIIb/IIIaan agonis lami iban[38]o sib a iban[39],aswellas ac o Xa
inhibi o s[40,41].
Becauseo ou pa en andpublica ionson hep od ugs a egy“amidoximesins ead
o amidines”,wewe eapp oachedbyAs aZeneca.Acommonp ojec s a ed oiden i y
heenzyme esponsible o  educ iono amidoximes oamidinessuchasximelaga an o
melaga an( idein a).
O pa icula no eis he ac o IIainhibi o ( h ombininhibi o )melaga an,whe e
heamidoximep od ugximelaga anhadano albioa ailabili yo 18–24%compa ed o
3–7% o  heac i ecompound[42,43].Ximelaga anwasanimpo an miles one,asi was
app o edin2003as he i s o  he“newo alan icoagulan s”(NOACs).Un o una ely,a
smallpo iono pa ien s ea edwi hximelaga anshowed ansien lyinc eased
asymp oma icli e  ansaminasele els[44],whiche en uallyled oacomple ema ke 
wi hd awalin2006[45].Ano he  ac o IIinhibi o ,dabiga an, emainsa ailable.Like
melaga an,dabiga anisaBAde i a i e(Figu e4)andisno o allybioa ailableini s
ac i e o m.Ins eado usinganamidoximep od ugapp oach, heamidinewas
inco po a edin oau e haneg oup,which eleases heac i eamidinea e abso p ionby
enzyma ichyd olysis[46].Howe e ,i shouldbeno ed ha wi h hiss a egy,o al
bioa ailabili yo  hep od ugdabiga ane exila e emainsqui elow(app ox.7%)[47],
e en houghanelabo a e o mula ionwasde eloped,inwhichdabiga ane exila eis
coa edin o a a icacidpelle s op o ideamic oacidicabso p ionen i onmen [48].We
Figu e 3.
Benzamidine binds o h ombin by o ming a sal b idge wi h aspa a e 189 in p oximi y
o he ca aly ic iad consis ing o se ine 195, his idine 57 and aspa a e 102, as can be seen in he
c ys al s uc u e o benzamidine-bound human h ombin (PDB: 4UEH) [
36
]. Panel (
A
): Ca oon
ep esen a ion. Panel (
B
): Elec os a ic su ace ep esen a ion. The elec os a ic po en ials we e
calcula ed wi h APBS [
37
] and a e ep esen ed as a colo g adien om ed—10 k
B
T/e
c
o e whi e
0 kBT/ec o blue +10 kBT/ec.
The BA moie y imi a ing he guanidine unc ional g oup o a ginine in he na u al
subs a e ib inogen is he e o e s ic ly equi ed o he pha macokine ic p ope ies o
hese no el an icoagulan d ugs and canno be eplaced by a less pola g oup. Howe e ,
he ee amidines usually lead o poo bioa ailabili y. In many cases, he amidoxime
p od ug p inciple can be applied success ully o inc ease he o al bioa ailabili y, e.g., o
he glycop o ein IIb/IIIa an agonis lami iban [
38
] o sib a iban [
39
], as well as ac o Xa
inhibi o s [40,41].
Because o ou pa en and publica ions on he p od ug s a egy “amidoximes ins ead
o amidines”, we we e app oached by As a Zeneca. A common p ojec s a ed o iden i y
he enzyme esponsible o educ ion o amidoximes o amidines such as ximelaga an o
melaga an ( ide in a).
O pa icula no e is he ac o IIa inhibi o ( h ombin inhibi o ) melaga an, whe e
he amidoxime p od ug ximelaga an had an o al bioa ailabili y o 18–24% compa ed o
3–7% o he ac i e compound [
42
,
43
]. Ximelaga an was an impo an miles one, as i
was app o ed in 2003 as he i s o he “new o al an icoagulan s” (NOACs). Un o u-
na ely, a small po ion o pa ien s ea ed wi h ximelaga an showed ansien ly inc eased
asymp oma ic li e ansaminase le els [
44
], which e en ually led o a comple e ma ke
wi hd awal in 2006 [
45
]. Ano he ac o II inhibi o , dabiga an, emains a ailable. Like
melaga an, dabiga an is a BA de i a i e (Figu e 4) and is no o ally bioa ailable in i s ac-
i e o m. Ins ead o using an amidoxime p od ug app oach, he amidine was inco po a ed
in o a u e hane g oup, which eleases he ac i e amidine a e abso p ion by enzyma ic
hyd olysis [
46
]. Howe e , i should be no ed ha wi h his s a egy, o al bioa ailabili y
o he p od ug dabiga an e exila e emains qui e low (app ox. 7%) [
47
], e en hough an
elabo a e o mula ion was de eloped, in which dabiga an e exila e is coa ed in o a a ic
acid pelle s o p o ide a mic oacidic abso p ion en i onmen [
48
]. We could demons a e
ha he amidoxime p od ug app oach wo ks jus as well o his amidine [49].
The amidoxime p od ug p inciple was shown o wo k o a se ies o o he amidines.
Examples a e he u okinase inhibi o upamos a [
50
], which has ecen ly been s udied as
a po en ial ea men agains SARS-CoV-2 [
51
], in es iga ional an i i al d ugs [
52
,
53
] o
no el ni ic oxide syn hase inhibi o s [54].
Mode n d ug de elopmen pipelines can p oduce d ug candida es wi h p ac ically
any unc ional g oups. P od ugs based on amidoximes emain an in e es ing app oach o
mo e a o able physicochemical and pha macokine ic p ope ies.
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coulddemons a e ha  heamidoximep od ugapp oachwo ksjus aswell o  his
amidine[49].

Figu e4.P od ugp incipleso ximelaga ananddabiga ane exila e.
Theamidoximep od ugp inciplewasshown owo k o ase ieso o he amidines.
Examplesa e heu okinaseinhibi o upamos a [50],whichhas ecen lybeens udiedas
apo en ial ea men agains SARS-CoV2[51],in es iga ionalan i i ald ugs[52,53]o 
no elni icoxidesyn haseinhibi o s[54].
Mode nd ugde elopmen pipelinescanp oduced ugcandida eswi hp ac ically
any unc ionalg oups.P od ugsbasedonamidoximes emainanin e es ingapp oach
o mo e a o ablephysicochemicalandpha macokine icp ope ies.
3.Disco e yo  hemARCEnzymeSys em
While he ehadbeenplen yo e idence ha  heoxida iono amidines owa ds
amidoximesisca alyzedbycy och omeP450monooxygenases,wedidno knowwhich
pa icula enzymeswe e esponsible o  he educ iono amidoximes oamidines.
In ac ,manyo he au ho shadp e iouslys udiedme abolic educ iono N-
hyd oxyla edcompounds.Fo example,Kadluba andZiegle iden i iedan“NADH-
Dependen N-Hyd oxyAmineReduc ase”inpigli e mic osomes.I becameclea  ha 
N- educ ionwasca alyzedbyacomplexo a leas  h eep o eins:cy och omeb5(CYB5),
i s la in-con aining educ aseanda hi d,uniden i iedcomponen .Thisunknown hi d
p o einhadnos onglyabso bingco ac o sandwasinsensi i e ooxygeno  ypical
cy och omeP450inhibi o s[55,56].Simila ly,N- educ ionhadp e iouslybeenobse ed
in a li e mi ochond ia[57,58].
O e  heyea s,manya emp swe emade osol e he“mys e yo  he hi dp o ein”,
whichca alyzesN- educ ion oge he wi hcy och omeb5andNADH-cy och omeb5
educ ase(NB5R).The ewe ediffe en po en ialcandida es,suchasacy och omeP450
sub amily2Dmembe [59],o s ea oyl-CoAdesa u ase[60,61],whicha ecapableo 
educingamidoximes oamidines,bu wi h e ylowcon e sion a es.Thus,i seemed
ha  heseenzymeswouldno be esponsible o  heex ensi ein i o educ ion.
Whenwein es iga ed educ iono amidoximesindiffe en subcellula  ac ions,we
ound ha  heN- educ i eac i i ywassigni ican lyhighe inmi ochond iacompa ed o
mic osomes.Fu he mo e,i couldbeshown ha N- educ i eac i i ywass ongly
en ichedinp epa a ionso  heou e mi ochond ialmemb ane(OMM).
E en ually,myPhDs uden An jeHa emeye wasable odisco e  he“ hi d
p o ein”in2006.Th ougha igo ouslyimp o edpu i ica ionp o ocol,shewasable o
inallyisola e he hi dcomponen o  hemi ochond ialamidoxime- educingcomplex
andiden i yi bymassspec ome ic echniques.I was u he mo edisco e ed ha ou 
Figu e 4. P od ug p inciples o ximelaga an and dabiga an e exila e.
3. Disco e y o he mARC Enzyme Sys em
While he e had been plen y o e idence ha he oxida ion o amidines owa ds
amidoximes is ca alyzed by cy och ome P450 monooxygenases, we did no know which
pa icula enzymes we e esponsible o he educ ion o amidoximes o amidines.
In ac , many o he au ho s had p e iouslys udied me abolic educ ion o N-hyd oxyla ed
compounds. Fo example, Kadluba and Ziegle iden i ied an “NADH-Dependen N-Hyd oxy
Amine Reduc ase” in pig li e mic osomes. I became clea ha N- educ ion was ca alyzed by
a complex o a leas h ee p o eins: cy och ome b5 (CYB5), i s la in-con aining educ ase and
a hi d, uniden i ied componen . This unknown hi d p o ein had no s ongly abso bing co-
ac o s and was insensi i e o oxygen o ypical cy och ome P450 inhibi o s [
55
,
56
]. Simila ly,
N- educ ion had p e iously been obse ed in a li e mi ochond ia [57,58].
O e he yea s, many a emp s we e made o sol e he “mys e y o he hi d p o ein”,
which ca alyzes N- educ ion oge he wi h cy och ome b5 and NADH-cy och ome b5
educ ase (NB5R). The e we e di e en po en ial candida es, such as a cy och ome P450
sub amily 2D membe [
59
], o s ea oyl-CoA desa u ase [
60
,
61
], which a e capable o
educing amidoximes o amidines, bu wi h e y low con e sion a es. Thus, i seemed
ha hese enzymes would no be esponsible o he ex ensi e in i o educ ion.
When we in es iga ed educ ion o amidoximes in di e en subcellula ac ions, we
ound ha he N- educ i e ac i i y was signi ican ly highe in mi ochond ia compa ed
o mic osomes. Fu he mo e, i could be shown ha N- educ i e ac i i y was s ongly
en iched in p epa a ions o he ou e mi ochond ial memb ane (OMM).
E en ually, my PhD s uden An je Ha emeye was able o disco e he “ hi d p o ein”
in 2006. Th ough a igo ously imp o ed pu i ica ion p o ocol, she was able o inally isola e
he hi d componen o he mi ochond ial amidoxime- educing complex and iden i y i
by mass spec ome ic echniques. I was u he mo e disco e ed ha ou newly ound
“mi ochond ial amidoxime educing componen ” (mARC) con ained molybdenum co ac-
o (Moco) and is homologous o molybdenum co ac o sul u ase [
62
]. All mammalian
genomes encode wo pa alogues o mARC, mARC1 and mARC2. P io o he disco e y o
mARC, he genes we e called MOSC1 and MOSC2, as hey belong o a di e se supe amily
o p o eins e e ed o as “MOSC domain p o eins” [
63
]. The gene names we e acco dingly
changed o MARC1 and MARC2. Recen ly, he HUGO Gene Nomencla u e Commi ee
decided o change he gene names o MTARC1 and MTARC2, as MARC1 and MARC2 a e
commonly misin e p e ed as da es (1 Ma ch/2 Ma ch) by Mic oso O ice Excel (Mic oso ,
Redmond, WA, USA) [64].
A his poin , I had been a medicinal chemis wi h a ocus on d ug me abolism and
did no know much abou molybdenum and i s biochemis y. We he e o e wen looking
o collabo a o s wi h expe ise in hese ma e s and go in ouch wi h Ral Mendel and
Flo ian Bi ne , who had been s udying molybdenum enzymes and he molybdenum
co ac o biosyn hesis a TU B aunschweig o a long ime [
65
]. They in oduced me o he

Molecules 2023,28, 4713 6 o 14
molybdenum communi y, and I am uly g a e ul o he p oduc i e collabo a ion ha my
g oup main ained wi h Ral and Flo ian o many yea s.
Toge he wi h Ral and Flo ian, we we e able o p epa e mARC enzymes ecombi-
nan ly and p o e hei N- educ i e ac i i y in econs i u ed
in i o
HPLC-based ac i i y
assays [
66
,
67
]. O e he yea s, al e na i e mARC ac i i y assays ha e been de eloped, e.g.,
an assay based on pho ome ic measu emen o NADH consump ion [
68
] o di e en elec-
ochemical sys ems [
69
,
70
], de eloped in collabo a ion wi h he g oup o Paul Be nha d
in B isbane.
I was con i med ha mARC is localized in he OMM [
71
], and
N
- educ i e ac i -
i y equi es he mi ochond ial iso o m o CYB5 (CYB5B), no he mic osomal iso o m
(CYB5A) [
72
], and ha he ele an iso o m o NB5R is NB5R3 [
73
]. Figu e 5depic s
he pu a i e elec on low om NADH o an N-oxygena ed p oduc ia CYB5, NB5R
and mARC.
Molecules2023,28,xFORPEERREVIEW6o 15


newly ound“mi ochond ialamidoxime educingcomponen ”(mARC)con ained
molybdenumco ac o (Moco)andishomologous omolybdenumco ac o sul u ase[62].
Allmammaliangenomesencode wopa alogueso mARC,mARC1andmARC2.P io  o
hedisco e yo mARC, hegeneswe ecalledMOSC1andMOSC2,as heybelong oa
di e sesupe amilyo p o eins e e ed oas“MOSCdomainp o eins”[63].Thegene
nameswe eacco dinglychanged oMARC1andMARC2.Recen ly, heHUGOGene
Nomencla u eCommi eedecided ochange hegenenames oMTARC1andMTARC2,
asMARC1andMARC2a ecommonlymisin e p e edasda es(1Ma ch/2Ma ch)by
Mic oso OfficeExcel(Mic oso ,Redmond,WA,USA)[64].
A  hispoin ,Ihadbeenamedicinalchemis wi ha ocusond ugme abolismand
didno knowmuchabou molybdenumandi sbiochemis y.We he e o ewen looking
o collabo a o swi hexpe isein hesema e sandgo in ouchwi hRal Mendeland
Flo ianBi ne ,whohadbeens udyingmolybdenumenzymesand hemolybdenum
co ac o biosyn hesisa TUB aunschweig o along ime[65].Theyin oducedme o he
molybdenumcommuni y,andIam ulyg a e ul o  hep oduc i ecollabo a ion ha 
myg oupmain ainedwi hRal andFlo ian o manyyea s.
Toge he wi hRal andFlo ian,wewe eable op epa emARCenzymes
ecombinan lyandp o e hei N- educ i eac i i yin econs i u edin i oHPLC-based
ac i i yassays[66,67].O e  heyea s,al e na i emARCac i i yassaysha ebeen
de eloped,e.g.,anassaybasedonpho ome icmeasu emen o NADHconsump ion[68]
o diffe en elec ochemicalsys ems[69,70],de elopedincollabo a ionwi h heg oupo 
PaulBe nha d inB isbane.
I wascon i med ha mARCislocalizedin heOMM[71],andN- educ i eac i i y
equi es hemi ochond ialiso o mo CYB5(CYB5B),no  hemic osomaliso o m
(CYB5A)[72],and ha  he ele an iso o mo NB5RisNB5R3[73].Figu e5depic s he
pu a i eelec on low omNADH oanN-oxygena edp oduc  iaCYB5,NB5Rand
mARC.

Figu e5.Pu a i eelec on anspo chaino  hemammalianmARCenzymesys em.Figu ec ea ed
wi hBioRende .
Ag ea miles onein ecen mARC esea chwas hesuccess ulde e mina iono  he
mARC1c ys als uc u ein2018[74].A  ha poin ,Ihadal eadys a eda e y ui ul
collabo a ionwi h heAxelScheidigg oupa KielUni e si y’ss uc u albiology
depa men ,bu  hemARCenzymep o ed e ydifficul  oc ys allize.E en ually, he
s uc u ecouldbede e minedusinganin e nal usionp o einapp oachwi hT4
lysozyme[75].Theex ensi eandsuccess ulcollabo a ionisongoingunaba ed.

Figu e 5.
Pu a i e elec on anspo chain o he mammalian mARC enzyme sys em. Figu e c ea ed
wi h BioRende .
A g ea miles one in ecen mARC esea ch was he success ul de e mina ion o he
mARC1 c ys al s uc u e in 2018 [
74
]. A ha poin , I had al eady s a ed a e y ui ul
collabo a ion wi h he Axel Scheidig g oup a Kiel Uni e si y’s s uc u al biology depa -
men , bu he mARC enzyme p o ed e y di icul o c ys allize. E en ually, he s uc u e
could be de e mined using an in e nal usion p o ein app oach wi h T4 lysozyme [
75
]. The
ex ensi e and success ul collabo a ion is ongoing unaba ed.
4. Subs a es o mARC
While mARC enzymes we e ini ially disco e ed h ough he educ ion o benza-
midoxime, many o he subs a es ha e been s udied o e he yea s. We ha e es ed a
g ea a ie y o subs i u ed benzamidoxime de i a i es [
76
] and we e unable o spo any
clea s uc u e–ac i i y ela ionships. mARC also educes N-hyd oxyguanidines such as
N
ω
-hyd oxy-L-a ginine [
77
] o guanoxabenz [
78
], N-hyd oxy sul onamides such as N-
hyd oxy-benzenesul onamide o N-hyd oxy- aldecoxib [
79
] and N-hyd oxamic acids such
as benzhyd oxamic acid, o inos a o bu examac [
80
]. N-oxides such as nico inamide N-
oxide [
78
] can also be educed; e en ime hylamine N-oxide, albei wi h e y low u no e
a es [81].
In d ug me abolism, much a en ion is usually paid owa ds oxida ions, bu educ ions,
like hose ca alyzed by mARC enzymes, should also be conside ed. Pa icula ly o ni ogen-
con aining unc ional g oups, educ ions a e as impo an as oxida ions [
82
]. mARC is
a d ug-me abolizing enzyme, as i can ac i a e N-hyd oxyla ed p od ugs ( ide sup a).
Howe e , mARC can also inac i a e d ug subs ances when hey ely on unc ional g oups
inco po a ing N-OH bonds. Fo example, hyd oxamic acids can be used in pha macopho es
a ge ing me allop o eins. This concep is used o inhibi o s o zinc-con aining his one
Molecules 2023,28, 4713 7 o 14
deace ylase [
83
], o he ma ix me allop o einase-13 inhibi o CP-544439. Some examples
o known mARC subs a es a e shown in Figu e 6.
Molecules2023,28,xFORPEERREVIEW7o 15
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
4.Subs a eso mARC
WhilemARCenzymeswe eini iallydisco e ed h ough he educ iono 
benzamidoxime,manyo he subs a esha ebeens udiedo e  heyea s.Weha e es ed
ag ea  a ie yo subs i u edbenzamidoximede i a i es[76]andwe eunable ospo any
clea s uc u e–ac i i y ela ionships.mARCalso educesN-hyd oxyguanidinessuchas
N
ω
-hyd oxy-
L
-a ginine[77]o guanoxabenz[78],N-hyd oxysul onamidessuchasN-
hyd oxy-benzenesul onamideo N-hyd oxy- aldecoxib[79]andN-hyd oxamicacids
suchasbenzhyd oxamicacid, o inos a o bu examac[80].N-oxidessuchas
nico inamideN-oxide[78]canalsobe educed;e en ime hylamineN-oxide,albei wi h
e ylow u no e  a es[81].
Ind ugme abolism,mucha en ionisusuallypaid owa dsoxida ions,bu 
educ ions,like hoseca alyzedbymARCenzymes,shouldalsobeconside ed.
Pa icula ly o ni ogen-con aining unc ionalg oups, educ ionsa easimpo an as
oxida ions[82].mARCisad ug-me abolizingenzyme,asi canac i a eN-hyd oxyla ed
p od ugs( idesup a).Howe e ,mARCcanalsoinac i a ed ugsubs anceswhen hey
elyon unc ionalg oupsinco po a ingN-OHbonds.Fo example,hyd oxamicacidscan
beusedinpha macopho es a ge ingme allop o eins.Thisconcep isused o inhibi o s
o zinc-con aininghis onedeace ylase[83],o  hema ixme allop o einase-13inhibi o 
CP-544439.Someexamples o knownmARCsubs a esa eshowninFigu e6.

Figu e6.Someexamples o mARCsubs a es.
Figu e 6. Some examples o mARC subs a es.
Simila ly, he cy os a ic agen N-hyd oxyu ea, an inhibi o o ibonucleo ide educ ase,
is used in sickle-cell disease and ce ain ypes o cance and is an excellen subs a e o
mARC1 [68], which is likely he eason o i s e y sho hal -li e ime [84].
Ano he aspec wo h conside ing is he de oxi ica ion eac ions ca alyzed by mARC.
Sho ly a e ou disco e y o mammalian mARC enzymes, Kozmin e al. disco e ed
ha wo mARC homologues, YiiM and YcbX, con ibu e owa ds esis ance o Esche ichia
coli bac e ia owa ds 6-hyd oxylaminopu ine [
85
]. Simila ly, mARC enzymes ha e been
shown o educe mu agenic N-hyd oxyla ed nucleobases and nucleo ides [
86
] and p o ec
cells agains hei ha m ul e ec s [
87
]. Toxic N-hyd oxyla ed me aboli es a e o en o med
in i o
. Fo example, sul ame hoxazole is oxidized
in i o
o a oxic hyd oxylamine, which
can be de oxi ied by mARC [88].
The analgesic d ug phenace in is me abolically oxidized o he hyd oxamic acid N-
hyd oxyphenace ine, a s ongly mu agenic compound held esponsible o phenace in’s se e e
side e ec s [
89
], which ha e led o i s wi hd awal om he ma ke . N-hyd oxyphenace ine
is no educed by mARC [
80
]. We ha e long hypo hesized ha any exogenous compounds
possessing ni ogen g oups ha can unde go me abolic oxida ion a e po en ially oxic, unless
hey can be de oxi ied by mARC o ano he mechanism.
I should be emphasized hough ha N- educ ion by mARC can also, in e y speci ic
cases, lead o oxi ica ion. Py olizidine alkaloids a e used by many plan s as a de ense
Molecules 2023,28, 4713 8 o 14
agains he bi o es. These alkaloids a e inac i e as N-oxides bu highly oxic in hei amine
o m. We could show ha seneci e nine N-oxide can be educed by mARC o elease he
oxic seneci e nine amine. In his case, oxida ion, i.e., by la in-con aining monooxygenases
o cy och ome P450 enzymes, would p esen a de oxi ica ion, bu educ ion by mARC a
oxi ica ion [68].
Whe he o no any o he unc ional g oups we ha e shown o be educed by mARC
ha e any connec ion o he enzymes’ physiological unc ion is cu en ly unknown. I has
been hypo hesized ha mARC migh play a ole in ni ic oxide homeos asis, ei he by
educing he ni ic oxide p ecu so [
77
] o by ac ing as a ni i e-dependen ni ic oxide
syn hase, i.e., ca alyzing a one-elec on educ ion o ni i e o ni ic oxide [
90
]. Whe he
his eac ion is ele an unde physiological condi ions emains unclea , as i appea s o
occu only unde anae obic condi ions [90,91].
5. mARC Enzymes in Human Disease
So a , we ha e mos ly looked a mARC as an enzyme in ol ed in me abolism o
xenobio ics. Mo e and mo e, howe e , i appea s ha mARC enzymes migh ha e unc ions
ela ed o physiological p ocesses and a e in ol ed in human disease.
One e y in e es ing case is he in ol emen o mARC in hepa ocellula ca cinoma
(HCC). I was ound ha mARC2 could supp ess he p og ession o HCC, due o compe-
i ion wi h he umo supp esso p o ein p27 o deg ada ion by he same ubiqui in E3
ligase RNF123 [
92
]. We ind his mechanism e y in e es ing as i is p esumably comple ely
un ela ed o mARC2’s enzyma ic ac i i y and he e o e ep esen s a ue moonligh ing
unc ion. O he au ho s ha e p e iously sugges ed ha mARC p o eins migh be moon-
ligh ing p o eins ul illing mul iple physiological unc ions [
93
]. A ollow-up s udy ound
a nega i e co ela ion be ween exp ession le els o MTARC2,CYB5 and NB5R wi h HCC
umo size, p og ession and isk o me as asis. I was sugges ed ha exp ession le els o
MTARC2
and i s elec on ca ie p o eins could se e as a p ognos ic ma ke in pa ien s
wi h HCC [94].
Righ now, he big s o y, howe e , is he in ol emen o mARC1 in li e disease, mo e
speci ically in non-alcoholic a y li e disease (NAFLD) and non-alcoholic s ea ohepa i is
(NASH). In 2020, Emdin e al. published a genome-wide associa ion s udy (GWAS) in
which he common p.A165T a ian o human mARC1 appea ed o con ey a p o ec i e
e ec agains li e ci hosis, dec ease li e a , ci cula ing li e enzymes and blood choles-
e ol le els [
95
]. An in ol emen o mARC enzymes in lipogenesis had been desc ibed
p e iously [
96
,
97
]. MTARC2 knockou mice possess a e y dis inc i e pheno ype: The
animals a e esis an o body weigh gain induced by a high- a die and ha e lowe blood
choles e ol le els [98,99], p o ing ha mARC has a c ucial unc ion in lipid me abolism.
None heless, he esul s o Emdin e al. ega ding he mARC1 a ian came as a
su p ise o us, as we had s udied he in luence o a ious common mu a ions on he
in i o
ac i i ies and molybdenum con en s o mARC enzymes yea s ea lie . In his s udy, he
mARC1 p.A165T a ian did no ha e al e ed ca aly ic p ope ies [
16
]. The mu a ed esidue
A165 is some 25 Å away om he ac i e si e o mARC1, and despi e some in silico s udies
sugges ing ha he a ian p o ein would “cause loss o he alpha-helix and al e he me al-
binding abili y o MTARC1” as well as “a ec he o e all s abili y o he p o ein” [
100
], ou
own X- ay c ys allog aphic analysis o he a ian p o ein e ealed no s uc u al di e ences
be ween he wild ype and a ian [
101
]. The mechanism by which he mARC1 p.A165T
a ian in luences li e disease emains unknown, and i migh equi e signi ican e o s
o unde s and i [102].
No wi hs anding, he connec ion be ween mARC1 and li e disease has been con-
i med by nume ous o he GWAS [
100
,
103
–
108
]. NAFLD is a e y p e alen disease; he
numbe o pa ien s a ec ed by NAFLD in he Uni ed S a es alone is expec ed o exceed
100 million by 2030, wi h 27% o hese cases p og essing o NASH. The e a e, as o ye , no
pha maco he apeu ic op ions o he ea men and p e en ion o NAFLD and NASH [
109
].
Molecules 2023,28, 4713 9 o 14
mARC1 migh ep esen an in e es ing d ug a ge , especially in obese pa ien s wi h
a high isk o li e mo ali y [
103
,
108
]. Consequen ly, many pha maceu ical companies
a e cu en ly in es iga ing si-RNA-based app oaches o a ge ed educ ion o mARC1
exp ession le els in he li e (see Table 1).
Table 1.
Recen pa en s ega ding mARC1 as a a ge o he p e en ion and/o ea men o
li e disease.
Pa en Numbe Company Ti le
WO2023282704 OliX Pha maceu icals Asymme ic siRNA a ge ing MARC1 gene, and use he eo
WO2022248665 No o No disk Composi ions and me hods o inhibi ing mi ochond ia
amidoxime- educing componen 1 (MARC1) exp ession
WO2022183065 Ionis Pha maceu icals Modula ion o MARC1 exp ession using an isense
oligonucleo ides o o he inhibi o s o ea li e disease
WO2022159158 Alnylam Pha maceu icals Modi ied double-s anded oligonucleo ides
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6. Ou look
O e he cou se o he yea s, ou iew on mARC enzymes has changed signi ican ly.
In he beginning, he enzymes we e mos ly o in e es wi h ela ion o he ac i a ion o
amidoxime p od ugs. As we go o lea n mo e abou mARC, we iewed i mo e as a
me abolic enzyme in ol ed in bio ans o ma ion eac ions o xenobio ics. Mo e ecen ly,
he ocus has shi ed owa ds he in ol emen o mARC enzymes in human disease,
pa icula ly, NAFLD and NASH. I will be exci ing o lea n mo e abou he ole o mARC
in disease and whe he o no mARC, in ac , will one day become a a ge o he apeu ic
d ugs. Table 2gi es a e y b ie summa y o he mos impo an miles ones in he s o y o
human mARC enzymes.
Table 2. Impo an miles ones in he s o y o human mARC enzymes.
Yea Disco e y Ci a ion
1983 BA is oxidized o BAO in i o [2]
1988 N- educ ion o BAO o BA is demons a ed in i o [21]
1993 In i o s udies show ha N- educ ion o BAO domina es physiologically [23]
2003 The mARC-ac i a ed p od ug Ximelaga an is submi ed o he FDA o app o al [110]
2005 N- educing ac i i y is highes in mi ochond ia [111]
2006 mARC p o eins we e i s isola ed om po cine li e [62]
2010 De ailed desc ip ion o ecombinan human mARC p o eins [67]
2017 Ini ial de elopmen o an elec ochemical assay o mARC ac i i y [69]
2018 C ys al s uc u e o human mARC1 [74,75]
2019 In i o mu ine MTARC2 knockou model unde sco es mARC’s ole in lipid me abolism [98]
2019 De elopmen o a as spec opho ome ic mARC ac i i y assay [68]
2020 The mARC1 p.A165T a ian is i s shown o p o ec agains li e disease [95]