INHIBITION OF XANTHINE-OXIDASE BY SYNTHETIC CYTOKININ ANALOGS

Thirteen synthetic cytokinin analogues were tested for their inhibitor y effects on xanthine oxidase. The enzyme, xanthine oxidase catalyses the oxidation of hypoxanthine to xanthine and of xanthine to uric acid , which has a lambda max of 295 nm forming the basis for a spectrophot ometric assay of the activity of xanthine oxidase. The results showed that 8-azaadenine(1), 4-amino-6-hydroxypyrazolo [3,4-d] pyrimidine(4), 4-amino-6-mercaptopyrazolo [3,4-d] pyrimidine(5) and 4-aminopyrazolo [3,4-d] pyrimidine(6) display inhibitory effects on xanthine oxidase w ith an order of activity of IC50= 0.54, 5.91, 8.17 and 25.46 mu M, res pectively. Their apparent inhibition constants (Ki) were 0.66, 1.54, 6 .61 and 26.79 mu M, and induced mixed (competitive-non-comptetitive), competitive, mixed (competitive-non-competitive), and competitive type s of inhibition.