Studies on the Biochemistry of Human Semen.:Some Properties of Prostatic Phosphatase.

Abstract

Summary.The enzymatic hydrolysis of phosphoryl choline, the natural substrate of human prostatic phosphatase, jS‐glycerophosphate and phenyl phosphate has been studied.1) The optimum pH when measured in acetate buffer solutions of constant ionic strength, is found to be about 6.0 for glycerophosphate and phenyl phosphate, and about 6.3 for phosphoryl choline.2) Fluoride, zinc chloride, oxalate and maleinate are found to inhibit the enzyme to a varying degree. Citrate to some extent abolishes this inhibition, and furthermore increases the reaction velocity of glycerophosphate and, especially, phosphoryl choline hydrolysis, also when prostatic secretion or seminal plasma is used without added inhibitor.3) The energy of activation is found to be about 11,500 cal for each of the three processes.4) The affinities between enzyme and substrate were measured at 37° and 0°. For phosphoryl choline and glycerophosphate it is about 2,500 cal/mol (37°), and for phenyl phosphate about 4,200 cal/mol. The change in heat function is small (δH = 0 ± 1,500 cal/mol).