The Competitive Inhibition of Uricase by Oxonate and by Related Derivatives of S-triazines.

The effect on enzyme kinetics of the presence of competitive inhibitors in constant molar ratio to t’he substrate has been described by Tubbs (I) and by Dalziel (2, 3). In this as yet unfamiliar situation, the inhibitor has the effect of increasing the apparent mutual affinity of enzyme and substrate. Thus, the slopes of reciprocal plots of the kinetic data are unchanged by the presence of the competitive inhibitor, whereas the ordinate intercepts are increased by a factor of [l + (K,R/Ki)], where R = [I]/[S]. At the inception of kinetic studies of purified hog liver uricase, a stock solution of urate was used which had been stored in the cold in dilute alkali for several months. The K, found with this aged urate was lower by an order of magnitude than that found with freshly prepared solutions of urate. In view of the work of Tubbs and of Dalziel, this suggested that aging in alkaline solution had converted some of the urate to a compound which is a potent competitive inhibitor of uricase. The identification of this inhibitor as oxonate (2,4-dihydroxy-6carboxy-s-triazine) and studies of the inhibition of uricase by oxonate and by related s-triazines form the body of this report.