The Effect of Copper on Urate Oxidase Activity

Abstract

1. The inactivation of crude extracts of urate oxidase was pH dependent. Enzyme solutions at pH > 10.0 inactivated rapidly on incubation at 40°. At pH values < 10.0 the enzyme was stable to incubation. Purified urate oxidase was stable to incubation at pH values > 10.0. 2. Crude urate oxidase solutions, ammonium sulphate-precipitated extracts and enzyme solutions purified by gel-filtration are all inactivated by copper at pH values > 10.0. Higher concentrations of Cu2+ were needed to give comparable inactivation for the crude extract compared with the purified enzyme. Below pH 10.0 the enzyme was stable. 3. Fe3+ had neither a retarding nor a promoting effect on inactivation of crude extracts containing copper. 4. The effects of incubation, copper and pH can be explained by either of the following hypotheses: (a) (i) assuming an inactivating factor is present in the crude extract, (ii) ionising groups, e.g., Є -amino of lysine, are involved in the active site. (b) (i) ionisation of groups on inert protein affect the stability of the protein and alter the conformation of the active site during incubation, (ii) changes in pH affect the ionisation of groups in the active site and alter the binding affinity for copper.