title: Effects of human cytochrome b5 on CYP3A4 activity and stability in vivo.
abstract: Cytochrome P450s (P450) form a superfamily of membrane-bound proteins that play a key role in the primary metabolism of both xenobiotics and endogenous compounds such as drugs and hormones, respectively. To be enzymically active, they require the presence of a second membrane-bound protein, NADPH P450 reductase, which transfers electrons from NADPH to the P450. Because of the diversity of P450 enzymes, much of the work on individual forms has been carried out on purified proteins, in vitro, which requires the use of complex reconstitution mixtures to allow the P450 to associate correctly with the NADPH P450 reductase. There is strong evidence from such reconstitution experiments that, when cytochrome b5 is included, the turnover of some substrates with certain P450s is increased. Here we demonstrate that allowing human P450 reductase, CYP3A4, and cytochrome b5 to associate in an in vivo-like system, by coexpressing all three proteins together in Escherichia coli for the first time, the turnover of both nifedipine and testosterone by CYP3A4 is increased in the presence of cytochrome b5. The turnover of testosterone was increased by 166% in whole cells and by 167% in preparations of bacterial membranes. The coexpression of cytochrome b5 also resulted in the stabilization of the P450 during substrate turnover in whole E. coli, with 109% of spectrally active CYP3A4 remaining in cells after 30 min in the presence of cytochrome b5 compared with 43% of the original P450 remaining in cells in the absence of cytochrome b5.
authors.affiliation: Biomedical Research Centre, Ninewells Hospital and Medical School, Dundee, DD1 9SY, United Kingdom.
authors.forename: M W
authors.initials: MW
authors.lastname: Voice
authors.forename: Y
authors.initials: Y
authors.lastname: Zhang
authors.forename: C R
authors.initials: CR
authors.lastname: Wolf
authors.forename: B
authors.initials: B
authors.lastname: Burchell
authors.forename: T
authors.initials: T
authors.lastname: Friedberg
mesh_terms: D003001:Cloning, Molecular; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D015786:Cytochromes b5 / Q000235:genetics / Q000378:metabolism*; D004795:Enzyme Stability; D004926:Escherichia coli / Q000235:genetics; D006801:Humans; D008658:Inactivation, Metabolic; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism*; D009543:Nifedipine / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D013739:Testosterone / Q000378:metabolism
chemical_list: D011994:Recombinant Proteins; D013739:Testosterone; D015786:Cytochromes b5; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D009543:Nifedipine