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. Author manuscript; available in PMC: 2015 Jan 1.
Published in final edited form as: Arch Biochem Biophys. 2013 Nov 17;541:53–60. doi: 10.1016/j.abb.2013.11.001

FIGURE 2.

FIGURE 2

Stimulation of CYP3A4-catalyzed testosterone 6β-hydroxylation and nifedipine oxidation by b5 and b5 mutations. Purified CYP3A4 (30 pmol) was reconstituted with POR, various b5 mutations, and CYMS as lipid for reconstitution. Catalytic activities toward (A) testosterone at 50 μM substrate concentration at a P450:POR:b5 molar ratio of 1:2:3 and (B) nifedipine at 200 μM substrate concentration at a P450:POR:b5 molar ratio of 1:2:4 were analyzed by HPLC. Results are shown as the percentage activity compared to wild-type b5 values (=100%) from duplicate determinations, means ± standard deviations. (C) Titration of CYP3A4-catalyzed testosterone 6β-hydroxylation with human cytochrome b5 mutation E48G/E49G. The stimulation of activity with P450:POR molar ratio of 1:2 reaches a maximum at a 3–5 molar excess of the b5 mutation and does not increase further.