Cytochrome b5 enhances androgen synthesis by rapidly reducing the CYP17A1 oxy‐complex in the lyase step

• Published in: FEBS letters Vol. 592; no. 13; pp. 2282 - 2288
• Main Authors: Duggal, Ruchia, Denisov, Ilia G., Sligar, Stephen G.
• Format: Journal Article
• Language: English
• Published: 01-07-2018
• Subjects: androgen biosynthesis; cytochrome b5; cytochrome P450; Nanodisc
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1002/1873-3468.13153

Cytochrome P450 17A1 (CYP17A1) catalyzes the synthesis of androgens from the steroid precursors pregnenolone and progesterone in a two‐step reaction process: allylic hydroxylation and carbo‐carbon bond scission. Cytochrome b5 (Cyt‐b5) is a stimulator of the second lyase reaction, but the chemical mechanism is unclear. We have shown previously that this stimulatory effect requires redox active Cyt‐b5. To investigate the origin of the lyase reaction enhancement by electron transfer from Cyt‐b5, we measured the reduction rates of oxy‐ferrous substrate‐bound CYP17A1 by Cyt‐b5 and by cytochrome P450 reductase (CPR) coincorporated in Nanodiscs using stopped flow spectroscopy. We observed that Cyt‐b5 reduces oxy‐ferrous CYP17A1 10‐fold faster than CPR, with the rate similar to that observed in a ternary complex of all three proteins.