Steroid Δ4-Reductases: their Physiological Role and Significance

This chapter discusses the steroid Δ⁴–reductases, the enzymes which catalyze the reduction of the double bond between carbons 4 and 5 of the steroid molecule, only mammalian steroids and mammalian enzymes. It reviews to indicate the physiological importance of Δ⁴–reduction in the overall disposition of steroid hormones and, in appropriate situations, how it affects biological actions of the parent compounds. The reduction of the double bond between carbons 4 and 5 of steroid molecules can either be the first step in a sequence of reactions leading to water–soluble conjugates which are excreted or result in the formation of compounds of key biological importance. The reduction of the double bond between steroid carbons 4 and 5 involves the addition of two hydrogen atoms. Progesterone is an important intermediate in the biosynthesis of both adrenocortical and gonadal steroid hormones.