American Association for Cancer Research

Table 1.

NADPH-supported E2 hydroxylation activities of human CYP1A1 variants

	2-OH-estradiol					4-OH-estradiol					6α-OH-estradiol
		V_max	K_m	V_max/K_m	V_max	K_m	V_max/K_m	V_max	K_m	V_max/K_m	V_max	K_m	V_max/K_m
CYP1A1.1	0.6 ± 0.1	9.5 ± 4.6	0.063	0.02 ± 0.002	11.8 ± 4.8	0.002	3.6 ± 0.8	79 ± 26	0.046	0.9 ± 0.1	19.6 ± 7.3	0.046
CYP1A1.2	3.3 ± 0.3	9.2 ± 2.3	0.359	0.08 ± 0.02	12.9 ± 6.5	0.006	1.3 ± 0.2	21.7 ± 6.2	0.060	9.3 ± 0.6	86 ± 8.0	0.108
CYP1A1.4	0.3 ± 0.03	9.8 ± 3.2	0.031	0.02 ± 0.002	12.3 ± 3.6	0.002	0.9 ± 0.1	18.6 ± 2.9	0.048	3.7 ± 0.6	89 ± 20	0.042

	2-OH-estradiol					4-OH-estradiol					6α-OH-estradiol
		V_max	K_m	V_max/K_m	V_max	K_m	V_max/K_m	V_max	K_m	V_max/K_m	V_max	K_m	V_max/K_m
CYP1A1.1	0.6 ± 0.1	9.5 ± 4.6	0.063	0.02 ± 0.002	11.8 ± 4.8	0.002	3.6 ± 0.8	79 ± 26	0.046	0.9 ± 0.1	19.6 ± 7.3	0.046
CYP1A1.2	3.3 ± 0.3	9.2 ± 2.3	0.359	0.08 ± 0.02	12.9 ± 6.5	0.006	1.3 ± 0.2	21.7 ± 6.2	0.060	9.3 ± 0.6	86 ± 8.0	0.108
CYP1A1.4	0.3 ± 0.03	9.8 ± 3.2	0.031	0.02 ± 0.002	12.3 ± 3.6	0.002	0.9 ± 0.1	18.6 ± 2.9	0.048	3.7 ± 0.6	89 ± 20	0.042

NOTE: NADPH-supported reactions were done in a reconstituted system consisting of purified human CYP1A1 variant, purified human P450 reductase and insect control microsomes. The final concentrations for determination of activities were 80 nmol/L, 400 nmol/L, and 320 μg/mL for CYP1A1, P450 reductase, and control microsomes, respectively. Formation of hydroxylated products was determined using HPLC and kinetic analyses were done by nonlinear regression as described under Materials and Methods.

V_max data are given in picomoles of product per minute/picomoles of CYP1A1, K_m data are in micromoles per liter, and catalytic efficiencies V_max/K_m are expressed in liter/micromoles per minute. Data represent mean ± SE as determined by nonlinear regression using software described under Materials and Methods.

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