The hydrolysis of phenyl phosphate by mouse-liver acid phosphatase

Abstract

An examination has been made of the effects of variations in assay conditions on the rate of hydrolysis of phenyl phosphate by mouse-liver acid phosphatase at 37[degree]. Maximum rates of hydrolysis were obtained with 0.1 [image]-phenyl phosphate (pH 5.9-6.1) and incubation periods of 5-10 min. There appeared to be no requirement for added metal ions. Inactivation of acid phosphatase shown to occur in liver homogenates incubated at pH 5.9 in both the absence and the presence of phenyl phosphate, was prevented by malonate. Evidence suggesting that enzyme inactivation is caused by traces of Fe3+ ions in liver homogenates is presented. Hydrolysis of phenyl phosphate was inhibited by Hg2+, Cu2+ and Fe3+ ions, p-chloromercuri- benzoate, phenyl mercuric acetate and o-iodosobenzoate, and these inhibitions were prevented by cysteine. This suggests that liver acid phosphate is a sulphydryl enzyme. Under optimum conditions of phenyl phosphate hydrolysis, fluoride, arsenate, phosphate, cyanide and pyro-phosphate caused significant enzyme inhibition, whereas citrate, [beta]-glycerophosphate, oxalate and L-tartrate had little effect. Inhibition by phosphate is shown to be competitive.