title: The mitochondrial Amidoxime Reducing Component (mARC) is involved in detoxification of N-hydroxylated base analogues.
abstract: The "mitochondrial Amidoxime Reducing Component" (mARC) is the newly discovered fourth molybdenum enzyme in mammals. All hitherto analyzed mammals express two mARC proteins, referred to as mARC1 and mARC2. Together with their electron transport proteins cytochrome b(5) and NADH cytochrome b(5) reductase, they form a three-component enzyme system and catalyze the reduction of N-hydroxylated prodrugs. Here, we demonstrate the reductive detoxification of toxic and mutagenic N-hydroxylated nucleobases and their corresponding nucleosides by the mammalian mARC-containing enzyme system. The N-reductive activity was found in all tested tissues with the highest detectable conversion rates in liver, kidney, thyroid, and pancreas. According to the presumed localization, the N-reductive activity is most pronounced in enriched mitochondrial fractions. In vitro assays with the respective recombinant three-component enzyme system show that both mARC isoforms are able to reduce N-hydroxylated base analogues, with mARC1 representing the more efficient isoform. On the basis of the high specific activities with N-hydroxylated base analogues relative to other N-hydroxylated substrates, our data suggest that mARC proteins might be involved in protecting cellular DNA from misincorporation of toxic N-hydroxylated base analogues during replication by converting them to the correct purine or pyrimidine bases, respectively.
authors.affiliation: Pharmaceutical Institute, Christian-Albrechts-University of Kiel, Germany 24118.
authors.forename: Nina
authors.initials: N
authors.lastname: Krompholz
authors.forename: Carmen
authors.initials: C
authors.lastname: Krischkowski
authors.forename: Debora
authors.initials: D
authors.lastname: Reichmann
authors.forename: Dieter
authors.initials: D
authors.lastname: Garbe-Schönberg
authors.forename: Ralf-R
authors.initials: RR
authors.lastname: Mendel
authors.forename: Florian
authors.initials: F
authors.lastname: Bittner
authors.forename: Bernd
authors.initials: B
authors.lastname: Clement
authors.forename: Antje
authors.initials: A
authors.lastname: Havemeyer
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D055162:Biocatalysis; D003562:Cytidine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D003596:Cytosine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D006801:Humans; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification
chemical_list: D024101:Mitochondrial Proteins; D011994:Recombinant Proteins; C021202:N(4)-hydroxycytosine; D003562:Cytidine; C030632:2-amino-N(6)-hydroxyadenine; D003596:Cytosine; C010737:N(4)-hydroxycytidine; D010088:Oxidoreductases; C554553:MTARC1 protein, human; C554552:mitochondrial amidoxime reducing component 2, human; D000225:Adenine