InterPro domain: IPR036374

A number of different eukaryotic oxidoreductases that require and bind a molybdopterin cofactor have been shown [ 1 ] to share a few regions of sequence similarity. These enzymes include xanthine dehydrogenase ( 1.1.1.204 ), aldehyde oxidase ( 1.2.3.1 ), nitrate reductase ( 1.7.1.1 ), and sulphite oxidase ( 1.8.3.1 ). The multidomain redox enzyme NAD(P)H:nitrate reductase (NR) catalyses the reduction of nitrate to nitrite in a single polypeptide electron transport chain with electron flow from NAD(P)H-FAD-cytochrome b5-molybdopterin-NO(3). Three forms of NR are known, an NADH-specific enzyme found in higher plants and algae ( 1.7.1.1 ); an NAD(P)H-bispecific enzyme found in higher plants, algae and fungi ( 1.7.1.2 ); and an NADPH-specific enzyme found only in fungi ( 1.7.1.3 ) [ 2 ]. The mitochondrial enzyme sulphite oxidase (sulphite:ferricytochrome c oxidoreductase; 1.8.2.1 ) catalyses oxidation of sulphite to sulphate, using cytochrome c as the physiological electron acceptor. Sulphite oxidase consists of two structure/function domains, an N-terminal haem domain, similar to cytochrome b5; and a C-terminal molybdopterin domain [ 3 ].

This domain contains a three layers beta-sheet structure and a beta-grasp like motif.

1. Enzymes depending on the pterin molybdenum cofactor: sequence families, spectroscopic properties of molybdenum and possible cofactor-binding domains. Biochim. Biophys. Acta 1057, 157-85
2. Functional domains of assimilatory nitrate reductases and nitrite reductases. Trends Biochem. Sci. 15, 315-9
3. Molecular basis of sulfite oxidase deficiency from the structure of sulfite oxidase. Cell 91, 973-83