The function and roles of P450c17 in androgen excess states

Cytochrome P450c17 is a multifunctional enzyme that converts C-21 steroids to the C-19 sex steroid precursor DHEA. Intuitively, increased expression o f P450c17 in the adrenals and ovaries might be expected to accompany androg en excess states, but the function of P450c17 in androgen biosynthesis is n ot so simple. The abundance of cofactor proteins and the coexistence of oth er enzymes contribute to the flux of precursor along pathways to different classes of active steroids. This paper explores the function of P450c17 in its proper biological context, using biochemical studies of patients with i solated 17,20-lyase activity to demonstrate key concepts in P450c17 enzymol ogy.