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Formation of 8-oxyadenine from adenine in bone marrow extracts

1954; Elsevier BV; Volume: 53; Issue: 1 Linguagem: Inglês

10.1016/0003-9861(54)90257-x

1096-0384

Marian Bentley, Richard Abrams,

Cytomegalovirus and herpesvirus research

This study directly compares the specificities of the structurally similar hydroxylating enzymes, aldehyde oxidase and xanthine oxidase. Michaelis-Menten constants for a variety of substrates of xanthine oxidase were in general lower than those of aldehyde oxidase. With respect to the rates of oxidation, the basic similarity was a preference for compounds having a substituted pyrimidine ring structure. Outstanding among the differences were the effects of the number and position of the ring substituents. Both enzymes readily oxidized a variety of unsubstituted and C-monosubstituted heterocycles, but only xanthine oxidase readily oxidized C-disubstituted derivatives. Certain N-substitutions, however, enhanced substrate activity with aldehyde oxidase, but markedly decreased it with xanthine oxidase. Although both enzymes preferred oxo over amino substituents, there were some specificity differences with respect to the chemical nature of substituents. Aldehyde oxidase, but not xanthine oxidase, tolerated 6-substitution of purine by alkyl, halogeno, cyano, or methylthio groups, while 6-hydroxyl or 6-methylamino substituents were tolerated only by xanthine oxidase. The position at which oxidation occurred was influenced by both the chemical nature and the positions of substituents. With some purines a different site was initially hydroxylated by each enzyme.