Xanthine oxidase inactivation by reagents that modify thiol groups.
1. The presence of xanthine was required for the inhibition of bovine milk xanthine oxidase by o-iodosobenzoate, iodoacetamide, hydrogen peroxide or p-chloromercuribenzoate. 2. Inactivation by p-chloromercuribenzoate was very rapid, was reversed by cysteine and was less in the presence of FAD. Lineweaver-Burk plots showed that the inactivation by p-chloromercuribenzoate was competitive with substrate. 3. Inactivation by o-iodosobenzoate, iodoacetamide or hydrogen peroxide could not be reversed by cysteine or xanthine. However, the presence of xanthine during the incubation with inhibitor protected the enzyme against o-iodosobenzoate but not against iodoacetamide or hydrogen peroxide. 4. p-Chloromercuribenzoate protected the enzyme against inactivation by hydrogen peroxide.
D000577:Amides; D000818:Animals; D001565:Benzoates; D002417:Cattle; D002729:Chloromercuribenzoates; D003545:Cysteine; D006861:Hydrogen Peroxide; D007455:Iodine; D007461:Iodoacetates; D007700:Kinetics; D008892:Milk / Q000201:enzymology*; D014969:Xanthine Oxidase / Q000037:antagonists & inhibitors*; D014970:Xanthines
D000577:Amides; D001565:Benzoates; D002729:Chloromercuribenzoates; D007461:Iodoacetates; D014970:Xanthines; D007455:Iodine; D006861:Hydrogen Peroxide; D014969:Xanthine Oxidase; D003545:Cysteine