TABLE 1

Parathion and chlorpyrifos metabolism by recombinant human P450s

Kinetic values are given for the metabolism of parathion and chlorpyrifos by recombinant human P450s. Values represent the mean ± S.E.M. of ^a n = 3, ^b n = 4, or ^c n = 6 experiments.

Cytochrome P450	K _m	V _max	V_max/K_m (CL_int)	K _m	V _max	V_max/K_m (CL_int)
		Paraoxon Formation			PNP Formation
	μM	pmol/min/nmol P450		μM	pmol/min/nmol P450
1A2^a	1.63 ± 0.13	6131 ± 90.1	3.755	2.15 ± 0.16	5656 ± 83.9	2.637
2B6^b	0.61 ± 0.08	4827 ± 134	7.875	0.74 ± 0.10	1804 ± 46.4	2.447
2C9^a	9.78 ± 1.63	1140 ± 47.7	0.117	12.1 ± 4.01	742 ± 63.3	0.061
2C19^a	0.56 ± 0.04	4879 ± 73.7	8.705	0.60 ± 0.09	2338 ± 65.4	3.872
3A4^a	65.5 ± 6.83	14,009 ± 767	0.214	31.2 ± 2.40	15,738 ± 488	0.504
3A5^b	43.2 ± 27.1	2020 ± 540	0.047	68.2 ± 121	1175 ± 1039	0.017
3A7^a				37.3 ± 10.6	1739 ± 201	0.047
		Chlorpyrifos Oxon Formation			TCP Formation
1A2^c	0.38 ± 0.53	1193 ± 143	3.131	0.63 ± 0.33	892 ± 51.7	1.416
2B6^a	0.81 ± 0.12	12,544 ± 418	15.560	2.09 ± 0.79	1545 ± 132	0.740
2C19^b	1.23 ± 1.20	2470 ± 485	2.013	1.63 ± 1.09	13,128 ± 2296	8.075
3A4^a	27.3 ± 5.04	11,946 ± 941	0.437	33.4 ± 10.0	12,667 ± 1758	0.379
3A5^a	16.6 ± 2.25	2569 ± 122	0.155	23.9 ± 9.87	2141 ± 354	0.090
3A7^a	34.0 ± 24.0	794 ± 252	0.023