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.

中文翻译：

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人线粒体偕胺肟还原成分 hmARC-1 和 hmARC-2 的生化和光谱表征表明真核生物中存在新的钼酶家族。

线粒体偕胺肟还原组分 mARC 是一种新发现的钼酶，推测它形成三组分酶系统的催化部分，该系统由 mARC、血红素/细胞色素 b(5) 和 NADH/FAD 依赖性细胞色素 b(5) 组成。 ）还原酶。mARC 蛋白与真核钼辅因子硫酸酶蛋白的钼辅因子结合域具有显着程度的同源性，后者催化醛氧化酶和黄嘌呤氧化还原酶的翻译后激活。人类基因组包含两个 mARC 基因，称为 hmARC-1/MOSC-1 和 hmARC-2/MOSC-2，它们在 1 号染色体上串联排列。 hmARC-1 和 hmARC-2 蛋白在大肠杆菌表明，这两种蛋白质的活性形式都是单体，这与所有其他作为同二聚体或异二聚体的真核钼酶形成鲜明对比。hmARC-1 和 hmARC-2 均催化多种 N-羟基化底物（例如 N-羟基胞嘧啶）的 N-还原，尽管具有不同的特异性。在没有硫的情况下，活性钼辅因子在重组 hmARC-1 和 hmARC-2 蛋白上的重建表明 mARC 蛋白不属于钼酶的黄嘌呤氧化酶家族。此外，它们似乎也不同于亚硫酸盐氧化酶家族，因为没有半胱氨酸残基可以被鉴定为钼原子的推定配体。这表明 hmARC 蛋白和硫酸酶代表了新的钼酶家族的成员。