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J Steroid Biochem Mol Biol. 2017 Jun;170:2-18. doi: 10.1016/j.jsbmb.2016.02.033. Epub 2016 Mar 11.

Role of cytochrome b5 in the modulation of the enzymatic activities of cytochrome P450 17α-hydroxylase/17,20-lyase (P450 17A1).

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Everest Biotech Pvt. Ltd., Khumaltar, Lalitpur, P.O. Box 21608, Kathmandu 44600, Nepal.
Institute of Biochemistry, Saarland University, 66123 Saarbrücken, Germany.
School of Medicine, Robinson Research Institute, University of Adelaide, Adelaide SA 5005, Australia.
School of Chemistry, Monash University, Clayton, 3800, Victoria, Australia. Electronic address:


Cytochrome b5 (cyt b5) is a small hemoprotein that plays a significant role in the modulation of activities of an important steroidogenic enzyme, cytochrome P450 17α-hydroxylase/17,20-lyase (P450 17A1, CYP17A1). Located in the zona fasciculata and zona reticularis of the adrenal cortex and in the gonads, P450 17A1 catalyzes two different reactions in the steroidogenic pathway; the 17α-hydroxylation and 17,20-lyase, in the endoplasmic reticulum of these respective tissues. The activities of P450 17A1 are regulated by cyt b5 that enhances the 17,20-lyase reaction by promoting the coupling of P450 17A1 and cytochrome P450 reductase (CPR), allosterically. Cyt b5 can also act as an electron donor to enhance the 16-ene-synthase activity of human P450 17A1. In this review, we discuss the many roles of cyt b5 and focus on the modulation of CYP17A1 activities by cyt b5 and the mechanisms involved.


20-lyase (P450 17A1, CYP17A1); Cytochrome P450 17α-hydroxylase/17; Cytochrome P450 oxido-reductase (CPR); Cytochrome b5 (cyt b5)

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