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Human Steroid Biosynthesis

Abstract:

Steroidogenesis is a directional process regulated through a variety of hormonal, cellular, and biochemical mechanisms. Only a few types of cells convert cholesterol to pregnenolone, the first committed step in steroidogenesis and the site of quantitative regulation. In these tissues, the downstream enzymes are deployed to efficiently complete the production of one or a few specific terminal products, with little accumulation of intermediates. General or composite pathways have been developed to summarize the possible fates of a given precursor steroid; however, the repertoire of enzymes expressed in each steroidogenic cell drives flux primarily along one characteristic pathway. In peripheral and target tissues, a variety of enzymatic processes can amplify, attenuate, or change the biological activities of the circulating steroid products of the adrenals, gonads, and placenta. In pathologic states, enzyme deficiencies cause the accumulation of intermediates and shunting of steroid precursors to alternate pathways, sometimes utilizing minor or secondary enzymes.