The function and roles of P450c17 in androgen excess states.

Cytochrome P450c17 is a multifunctional enzyme that converts C21 steroids to the C19 sex steroid precursor DHEA. Intuitively, increased expression of P450c17 in the adrenals and ovaries might be expected to accompany androgen excess states, but the function of P450c17 in androgen biosynthesis is not so simple. The abundance of cofactor proteins and the coexistence of other 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 isolated 17,20-lyase activity to demonstrate key concepts in P450c17 enzymology.