Purification of the aldehyde oxidase homolog 1 (AOH1) protein and cloning of the AOH1 and aldehyde oxidase homolog 2 (AOH2) genes - Identification ofa novel molybdo-flavoprotein gene cluster on mouse chromosome 1

We report the cloning of the AOH1 and AOH2 genes, which encode two novel ma mmalian molybdo-flavoproteins. We have purified the AOH1 protein to homogen eity in its catalytically active form from mouse liver. Twenty tryptic pept ides, identified or directly sequenced by mass spectrometry, confirm the pr imary structure of the polypeptide deduced from the AOH1 gene. The enzyme c ontains one molecule of FAD, one atom of molybdenum, and four atoms of iron per subunit and shows spectroscopic features similar to those of the proto typic molybdo-flavoprotein xanthine oxidoreductase. The AOH1 and AOH2 genes are 98 and 60 kilobases long, respectively, and consist of 35 coding exons . The AOH1 gene has the potential to transcribe an extra leader non-coding exon, which is located downstream of exon 26, and is transcribed in the opp osite orientation relative to all the other exons. AOH1 and AOH2 map to chr omosome I in close proximity to each other and to the aldehyde oxidase gene , forming a molybdo-flavoenzyme gene cluster. Conservation in the position of exon/intron junctions among the mouse AOH1, AOH2, aldehyde oxidase, and xanthine oxidoreductase loci indicates that these genes are derived from th e duplication of an ancestral precursor.