The enzymes and pathways of steroidogenesis are familiar to most endocrinologists, but the biochemistry and molecular biology of these processes are still being studied. This chapter outlines current knowledge about each enzyme. The quantitative regulation of steroidogenesis occurs at the first step, the conversion of cholesterol to pregnenolone. Chronic regulation is principally at the level of transcription of the gene for P450 side chain cleave (P450scc), which is the enzymatically rate-limiting step. Acute regulation is mediated by steroidogenic acute regulatory protein, which facilitates the rapid influx of cholesterol into mitochondria, where P450scc resides. Qualitative regulation, determining the class of steroid produced, is principally determined by P450c17. In the absence of P450c17 in the zona glomerulosa, C21 deoxy steroids are produced, leading to the mineralocorticoid aldosterone. In the presence of the 17-hydroxylase but not the 17,20 lyase activity of P450c17 in the zona fasciculata, C21, 17-hydroxy steroids are produced, leading to the glucocorticoid cortisol. When both the 17-hydroxylase and 17,20 lyase activities of P450c17 are present in the zona reticularis, the androgen precursor dehydroepiandrosterone is produced. The discrimination between 17-hydroxylase and 17,20 lyase activities is regulated by two posttranslational events, the serine phosphorylation of P450c17 and the allosteric action of cytochrome b5, both of which act to optimize the interaction of P450c17 with its obligatory electron donor, P450 oxidoreductase.
The StAR protein was first identified, characterized and named by Dr. Douglas Stocco at Texas Tech University Health Sciences Center in 1994.  The role of this protein in lipoid CAH was confirmed the following year in collaboration with Dr. Walter Miller at the University of California, San Francisco .  All of this work follows the initial observations of the appearance of this protein and its phosphorylated form coincident with factors that caused steroid production by Dr. Nanette Orme-Johnson while at Tufts University .