MOCOS

This gene encodes an enzyme that sulfurates the molybdenum cofactor which is required for activation of the xanthine dehydrogenase (XDH) and aldehyde oxidase (AO) enzymes. XDH catalyzes the conversion of hypoxanthine to uric acid via xanthine, as well as the conversion of allopurinol to oxypurinol, and pyrazinamide to 5-hydroxy pyrazinamide. Mutations in this gene cause the metabolic disorder classical xanthinuria type II which is characterized by the loss of XDH/XO and AO enzyme activity, decreased levels of uric acid in the urine, increased levels of xanthine and hypoxanthine in the serum and urine, formation of xanthine stones in the urinary tract, and myositis due to tissue deposition of xanthine.

molybdenum cofactor sulfurase

Sulfurates the molybdenum cofactor. Sulfation of molybdenum is essential for xanthine dehydrogenase (XDH) and aldehyde oxidase (ADO) enzymes in which molybdenum cofactor is liganded by 1 oxygen and 1 sulfur atom in active form. In vitro, the C-terminal domain is able to reduce N-hydroxylated prodrugs, such as benzamidoxime.

Molybdopterin cofactor biosynthetic process Source: Reactome
Molybdopterin cofactor metabolic process Source: UniProtKB
Mo-molybdopterin cofactor biosynthetic process Source: UniProtKB-UniRule

Cytosol

Xanthinuria 2 (XAN2):
A disorder characterized by excretion of very large amounts of xanthine in the urine and a tendency to form xanthine stones. Uric acid is strikingly diminished in serum and urine. In addition, XAN2 patients cannot metabolize allopurinol into oxypurinol due to dual deficiency of xanthine dehydrogenase and aldehyde oxidase.