title: Biochemical and spectroscopic characterization of the human mitochondrial amidoxime reducing components hmARC-1 and hmARC-2 suggests the existence of a new molybdenum enzyme family in eukaryotes.
abstract: The mitochondrial amidoxime reducing component mARC is a newly discovered molybdenum enzyme that is presumed to form the catalytical part of a three-component enzyme system, consisting of mARC, heme/cytochrome b(5), and NADH/FAD-dependent cytochrome b(5) reductase. mARC proteins share a significant degree of homology to the molybdenum cofactor-binding domain of eukaryotic molybdenum cofactor sulfurase proteins, the latter catalyzing the post-translational activation of aldehyde oxidase and xanthine oxidoreductase. The human genome harbors two mARC genes, referred to as hmARC-1/MOSC-1 and hmARC-2/MOSC-2, which are organized in a tandem arrangement on chromosome 1. Recombinant expression of hmARC-1 and hmARC-2 proteins in Escherichia coli reveals that both proteins are monomeric in their active forms, which is in contrast to all other eukaryotic molybdenum enzymes that act as homo- or heterodimers. Both hmARC-1 and hmARC-2 catalyze the N-reduction of a variety of N-hydroxylated substrates such as N-hydroxy-cytosine, albeit with different specificities. Reconstitution of active molybdenum cofactor onto recombinant hmARC-1 and hmARC-2 proteins in the absence of sulfur indicates that mARC proteins do not belong to the xanthine oxidase family of molybdenum enzymes. Moreover, they also appear to be different from the sulfite oxidase family, because no cysteine residue could be identified as a putative ligand of the molybdenum atom. This suggests that the hmARC proteins and sulfurase represent members of a new family of molybdenum enzymes.
authors.affiliation: Department of Plant Biology, Technische Universität Braunschweig, 38023 Braunschweig, Germany.
authors.forename: Bettina
authors.initials: B
authors.lastname: Wahl
authors.forename: Debora
authors.initials: D
authors.lastname: Reichmann
authors.forename: Dimitri
authors.initials: D
authors.lastname: Niks
authors.forename: Nina
authors.initials: N
authors.lastname: Krompholz
authors.forename: Antje
authors.initials: A
authors.lastname: Havemeyer
authors.forename: Bernd
authors.initials: B
authors.lastname: Clement
authors.forename: Tania
authors.initials: T
authors.lastname: Messerschmidt
authors.forename: Martin
authors.initials: M
authors.lastname: Rothkegel
authors.forename: Harald
authors.initials: H
authors.lastname: Biester
authors.forename: Russ
authors.initials: R
authors.lastname: Hille
authors.forename: Ralf R
authors.initials: RR
authors.lastname: Mendel
authors.forename: Florian
authors.initials: F
authors.lastname: Bittner
mesh_terms: D000818:Animals; D006801:Humans; D007700:Kinetics; D051379:Mice; D008928:Mitochondria / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D024101:Mitochondrial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008982:Molybdenum / Q000378:metabolism*; D005810:Multigene Family; D010088:Oxidoreductases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013057:Spectrum Analysis; D013379:Substrate Specificity; D050876:Sulfite Oxidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D024101:Mitochondrial Proteins; D008982:Molybdenum; D010088:Oxidoreductases; C534493:amidoxime reducing component, human; C554553:MTARC1 protein, human; C554552:mitochondrial amidoxime reducing component 2, human; D050876:Sulfite Oxidase