Regulation of Steroidogenic and Related P450s

Abstract

One broad classification of P450s is as two groups, one containing forms that metabolize endogenous substrates and the other, forms that metabolize exogenous substrates (xenobiotics). Those forms that metabolize endogenous substrates generally convert less active compounds into more active ones. This is particularly true of the P450s that participate in steroid hormone biosynthesis, where the less active steroid cholesterol is converted into more active mineralocorticoids, glucocorticoids, progestins, and sex hormones. Interestingly, hepatic P450s of the xenobiotic-metabolizing class may play important roles in inactivating these steroid hormones. In the case of vitamin D we also find that distinct P450s play roles in producing the most active forms of this hormone and other P450s are important in their inactivation. This chapter will summarize our understanding of the function and regulation of P450 systems involved in production of active steroids and related compounds.