Catalysis uric acid oxidation

NAD+. They catalyze the hydroxylation of purines. Equation (50) shows the xanthine oxidase-catalyzed oxidation of xanthine to uric acid. Xanthine oxidase is probably the most well-studied molybdenum enzyme. There is good evidence that the molybdenum is the site for binding and reduction of xanthine. The enzyme contains MoVI in the resting form, while MoIV and Mov are implicated during catalysis. 

Uric acid (Fig. 1) in the human body is the end product of purine metabolism. It is produced by the enzymatic conversion of hypoxanthine to xanthine and then to uric acid. The enzyme involved here is xanthine oxidoreductase. This enzyme exists in two forms xanthine dehydrogenase and xanthine oxidase. The latter is able to produce oxidizing species during enzymatic catalysis [4]. In most organisms uric acid is enzymatically degraded by an enzyme called urate... 

A number of eomputational studies have contributed to our understanding of the XOR and AO reaction coordinate. Figure 2.24 highlights the salient features of the XOR eatal)Tic cycle for the oxidation of xanthine to uric acid that are consistent with experimental data and the results of recent QMMM stud-iesi2.i3.i37 j ye probed the XOR and AO reaction coordinates. The results of these caleulations have converged on a mechanistic sequence whereby catalysis is initiated by nueleophilic attack of metal activated water ie. hydroxide) on the appropriate earbon atom of substrate. This is followed by the net formal transfer of a hydride at the tetrahedral transition state to the terminal sulfido of the [MoOS] eenter to yield bound product as the enolate tautomer and a reduced [MoOSH] site. The nature of the C-H bond activation process was... 

It is not possible to decide upon the basis of evidence now available whether primary catalysis in enzymic oxidation of uric acid involves transfer of two hydrogen atoms or of two electrons and a proton, but in either case a two-equivalent transfer takes place at the prosthetic surface of the enzyme. There is no evidence that free radicals are formed from the oxygen and the uric acid consumed. 

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