The cDNAs coding for two novel mouse molybdo-flavoproteins, AOH1 and AOH2 (aldehyde oxidase homolog 1 and 2), were isolated. The AOH1 and AOH2 cDNAs code for polypeptides of 1336 amino acids. The two proteins have similar primary structure and show striking amino acid identity with aldehyde oxidase and xanthine oxidoreductase, two other molybdo-flavoenzymes. AOH1 and AOH2 contain consensus sequences for a molybdopterin-binding site and two distinct 2Fe-2S redox centers. In its native conformation, AOH1 has a molecular weight consistent with a homotetrameric structure. Transfection of the AOH1 and AOH2 cDNAs results in the production of proteins with phenanthridine but not hypoxanthine oxidizing activity. Furthermore, the AOH1 protein has benzaldehyde oxidizing activity with electrophoretic characteristics identical to those of a previously identified aldehyde oxidase isoenzyme (Holmes, R. S. (1979) Biochem. Genet. 17, 517-528). The AOH1 transcript is expressed in the hepatocytes of the adult and fetal liver and in spermatogonia. In liver, the AOH1 protein is synthesized in a gender-specific fashion. The expression of AOH2 is limited to keratinized epithelia and the basal layer of the epidermis and hair folliculi. The selective cell and tissue distribution of AOH1 and AOH2 mRNAs is consistent with the localization of the respective protein products.
We report the cloning of the AOH1 and AOH2 genes, which encode two novel mammalian molybdo-flavoproteins. We have purified the AOH1 protein to homogeneity in its catalytically active form from mouse liver. Twenty tryptic peptides, identified or directly sequenced by mass spectrometry, confirm the primary structure of the polypeptide deduced from the AOH1 gene. The enzyme contains one molecule of FAD, one atom of molybdenum, and four atoms of iron per subunit and shows spectroscopic features similar to those of the prototypic 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 opposite orientation relative to all the other exons. AOH1 and AOH2 map to chromosome 1 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 the duplication of an ancestral precursor.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.