K. Kahn et al., IDENTIFICATION OF THE TRUE PRODUCT OF THE URATE OXIDASE REACTION, Journal of the American Chemical Society, 119(23), 1997, pp. 5435-5442
The O-2-dependent oxidation of urate catalyzed by urate oxidase has be
en examined in order to identify the immediate product of the enzymati
c reaction. Specifically labeled [C-13]urates were utilized as substra
tes, and the time courses were monitored by C-13 NMR. On the basis of
chemical shift values and O-18 labeling, the product of the reaction w
as identified as 5-hydroxyisourate. This identification was substantia
ted by calculation of the C-13 NMR spectrum of 5-hydroxyisourate using
ab initio density functional theory methods. The predominant tautomer
s of urate and allantoin in aqueous solution were identified from C-13
NMR titration data; the ionization behavior of urate and 5-hydroxyiso
urate were also examined by computational methods. The nonenzymatic pa
thway for production of allantoin from 5-hydroxyisourate was delineate
d; the reaction proceeds by the hydrolysis of the N1-C6 bond, followed
by an unusual 1,2-carboxylate shift and decarboxylation to form allan
toin.