Table 2

Effects of testosterone on bufuralol 1′-hydroxylase activities of membranes containing different combinations of CYP3A4, CYP2D6, and CPR

Incubation SystemBufuralol 1′-Hydroxylase ActivityActivity
nmol/min/nmol total P-450 %
CYP2D6/pJR78.54  ± 0.77100
CYP2D6/pJR7 + testosterone7.65  ± 0.3590
CYP2D6/pJR7 + 6β-hydroxytestosterone8.65  ± 0.52101
CYP3A4/CYP2D6/pJR73.75  ± 0.27100
CYP3A4/CYP2D6/pJR7 + testosterone2.15  ± 0.142-a 57
CYP3A4/CYP2D6/pDRlacZ0.42  ± 0.02100
CYP3A4/CYP2D6/pDRlacZ + testosterone0.15  ± 0.012-a 36

Membranes containing 10 pmol P-450 were incubated at 37°C for 10 min in 50 mM potassium phosphate buffer (pH 7.4), containing 10 μM bufuralol, and, when indicated, 100 μM testosterone. Reaction was initiated by addition of a NADPH-regenerating system (seeExperimental Procedures). Reaction was stopped by adding 15 μl 60% perchloric acid. Analysis of metabolites was by HPLC chromatography. Values are given as means of six experiments ±S.D. Incubations were also carried out in the presence of 6β-hydroxytestosterone (10 μM).

  • 2-a Significantly different from control p≤ .01, n = 6 independent experiments each in triplicate.