Requirements of the cholesterol side-chain-cleaving enzyme system of rat-testis mitochondria

Abstract

A 0.25 M sucrose suspension of a washed rat-testis mitochondrial preparation containing the cholesterol side-chain-cleaving enzyme system was incubated in the presence of TPNH and cyanide 1. It was most active when buffered with 0.02 M Tris-HCl buffer at pH 7.4 as compared with an 0.154 M KCl suspension buffered with 0.066 M phosphate buffer also at pH 7.4. Addition of either Mg 2+ or Ca 2+ resulted in a 7–8-fold increase in rate. In the presence of optimal levels of Ca 2+ (10 μmole), addition of 120 μmoles of KCl resulted in a further 30% increase in the rate of side-chain cleavage. Pre-treatment with gonadotropin of immature and mature rats resulted in a 6-fold increase in the rate in vitro of cholesterol side-chain cleavage by the isolated mitochondrial pellets. However, no effect was observed by gonadotropins added in vitro.