The Cholesterol Side-Chain Cleavage Enzymes in Steroid Hormone-Producing Tissues

Abstract

Publisher Summary This chapter discusses the cholesterol side-chain cleavage enzymes in steroid hormone-producing tissues. There is now little doubt that cholesterol is the obligatory precursor of steroid hormones produced by the ovary, testis, adrenal, and placenta. In these tissues, cholesterol can be metabolized to pregnenolone and progesterone, and the cleavage of the cholesterol side chain appears to be the first reaction in the degradation of cholesterol to steroid hormones. This cleavage reaction is common to all steroidogenic tissue and seems to involve hydroxylation of the cholesterol molecule at C-20 and C-22. This results in an overall side-chain cleavage leading to pregnenolone formation. The cholesterol side-chain cleavage enzyme system occurs in mitochondria and has the characteristics of a mixed-function oxidase requiring NADPH and molecular oxygen for its activity. The relevant enzymes have been resolved, and understanding of the components of the electron transport system in this mitochondrial reaction has recently been greatly extended.