Mechanism of the conversion of xanthine dehydrogenase to xanthine oxidase: identification of the two cysteine disulfide bonds and crystal structure of a non-convertible rat liver xanthine dehydrogenase mutant.

摘要: Mammalian xanthine dehydrogenase can be converted to oxidase by modification of cysteine residues or proteolysis the enzyme polypeptide chain. Here we present evidence that Cys535 and Cys992 rat liver are indeed involved in rapid conversion from oxidase. The purified mutants C535A and/or C992R were significantly resistant incubation with 4,4′-dithiodipyridine, whereas recombinant wild-type readily type, indicating these responsible for conversion. C535A/C992R mutant, however, very slowly during prolonged this slow was blocked addition NADH, suggesting another couple located near NAD+ binding site is slower On other hand, C535A/C992R/C1316S C535A/C992R/C1324S completely conversion, even on Cys1316 Cys1324 crystal structure mutant determined its demolybdo form, confirming conformation.