Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 1998 Feb 6;273(6):3158-65.
doi: 10.1074/jbc.273.6.3158.

Cytochrome b5 augments the 17,20-lyase activity of human P450c17 without direct electron transfer

R J Auchus  1 , T C Lee, W L Miller
Affiliations
Free article

Cytochrome b5 augments the 17,20-lyase activity of human P450c17 without direct electron transfer

R J Auchus et al. J Biol Chem. .
Free article

Abstract

In the biosynthesis of steroid hormones, P450c17 is the single enzyme that catalyzes both the 17alpha-hydroxylation of 21-carbon steroids and the 17,20-lyase activity that cleaves the C17-C20 bond to produce C19 sex steroids. Cytochrome b5 augments the 17,20-lyase activity of cytochrome P450c17 in vitro, but this has not been demonstrated in membranes, and the mechanism of this action is unknown. We expressed human P450c17, human P450-oxidoreductase (OR), and/or human cytochrome b5 in Saccharomyces cerevisiae and analyzed the 17alpha-hydroxylase and 17,20-lyase activities of the resulting yeast microsomes. Yeast expressing only P450c17 have 17alpha-hydroxylase and trace 17,20-lyase activities toward both Delta4 and Delta5 steroids. Coexpression of human OR with P450c17 increases the Vmax of both the 17alpha-hydroxylase and 17,20-lyase reactions 5-fold; coexpression of human b5 with P450c17 also increases the Vmax of the 17,20-lyase reactions but not of the 17alpha-hydroxylase reactions. Simultaneous expression of human b5 with P450c17 and OR, or addition of purified human b5 to microsomes from yeast coexpressing human P450c17 and OR, further increases the Vmax of the 17,20-lyase reaction without altering 17alpha-hydroxylase activity. Genetically engineered yeast and mixing experiments demonstrate that OR is both necessary and sufficient for microsomal 17,20-lyase activity. Addition of purified human holo-b5, apo-b5, or cytochrome c to microsomes containing both human P450c17 and OR demonstrate that the stimulatory action of b5 does not require electron transfer from b5 to P450c17. These data suggest that human b5 acts principally as an allosteric effector that interacts primarily with the P450c17.OR complex to stimulate 17, 20-lyase activity.

PubMed Disclaimer

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

Publication types

Substances

LinkOut - more resources