Intermediate dehydrogenase-oxidase form of xanthine oxidoreductase in rat liver.
A spectrophotometric method for the determination of three forms of xanthine oxidoreductase, namely dehydrogenase (D), dehydrogenase-oxidase (D/O) and oxidase (O), is described. Enzymic fractions obtained from rat liver were found to contain either all three forms, or (under special conditions of preparation) only two forms, D and D/O. The conversion of form D leads to form D/O leads to form O in the presence of Cu2+ ions was shown. Form D/O acted with NAD+ as well as with O2 as electron acceptors, it exhibited greater affinity to NAD+ than to O2, and NAD+ abolished the oxidase activity of this form. Moreover, oxidase activity of form D/O was inhibited by NADH. These facts indicate that NAD+ and O2 compete for the same active site on the enzyme molecule.
D000818:Animals; D055598:Chemical Phenomena; D002621:Chemistry; D003300:Copper / Q000494:pharmacology; D007658:Ketone Oxidoreductases / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D008297:Male; D009243:NAD / Q000378:metabolism; D010100:Oxygen; D051381:Rats; D013053:Spectrophotometry / Q000379:methods; D014968:Xanthine Dehydrogenase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014969:Xanthine Oxidase / Q000037:antagonists & inhibitors / Q000378:metabolism*
D009243:NAD; D003300:Copper; D014968:Xanthine Dehydrogenase; D014969:Xanthine Oxidase; D007658:Ketone Oxidoreductases; D010100:Oxygen