Table 1

Summary of Michaelis-Menten kinetic parameters for SN-38 formation from CPT-11 by human liver microsomes. V vs. [S] data for each donor were fit by nonlinear regression to a 2 enzyme Michaelis-Menten equation to obtain K_M and V_max estimates

Donor/Sex	Low K_MIsoform		High K_MIsoform
Donor/Sex	K_M (μM)	V_max (pmol/mg/min)	V_max/K_M	K_M (μM)	V_max (pmol/mg/min)	V_max/K_M
Pooled	2.4 ± 0.4	2.04 ± 0.30	0.86	146 ± 43	14.8 ± 2.0	0.10
10 M	1.5 ± 0.8	2.46 ± 0.56	1.63	129 ± 45	12.7 ± 1.5	0.10
15 M	2.7 ± 0.5	1.21 ± 0.20	0.44	164 ± 83	5.30 ± 1.3	0.03
24 M	1.4 ± 0.2	2.41 ± 0.23	1.72	150 ± 73	15.1 ± 4.6	0.10
Mean ± S.D.	1.9 ± 1.0	2.03 ± 0.64	1.26 ± 0.71	148 ± 120	11.0 ± 4.9	0.08 ± 0.04
9 F	3.9 ± 0.8	1.37 ± 0.27	0.35	150 ± 66	6.75 ± 1.2	0.04
17 F	1.4 ± 0.2	2.60 ± 0.21	0.84	150 ± 54	8.14 ± 1.4	0.05
20 F	2.9 ± 0.5	2.61 ± 0.39	0.89	150 ± 46	16.6 ± 2.3	0.11
Mean ± S.D.	2.7 ± 0.9	2.19 ± 0.52	0.69 ± 0.30	150 ± 97	10.5 ± 2.9	0.07 ± 0.04
Grand mean ± S.D.	2.3 ± 1.4	2.11 ± 0.82	0.98 ± 0.58	149 ± 154	10.8 ± 5.8	0.07 ± 0.04

M, male; F, female; SD calculated as root of sum of squared deviations/N.