Table 1

Kinetic parameters of BUP hydroxylation in select HLM preparations and in microsomes containing cDNA-expressed CYP2B6

Sample	Model Equation	K_m^1-a	V_max^1-a	n^1-a
		μM	pmol/min/mg protein
HLM 13	Hill	168.0 ± 17.3 (10.3%)	98.7 ± 4.0 (4.0%)	1.3 ± 0.1 (8.3%)
HLM 14	Hill	162.7 ± 10.6 (6.5%)	82.0 ± 2.0 (2.5%)	1.3 ± 0.05 (4.1%)
HLM 16	Hill	167.6 ± 12.2 (7.3%)	2450.7 ± 64.3 (2.6%)	1.2 ± 0.04 (3.4%)
HLM 17	Hill	77.6 ± 7.8 (10.1%)	648.2 ± 22.1 (3.4%)	1.4 ± 0.1 (7.4%)
HLM 25	Hill	75.3 ± 7.0 (9.2%)	418.0 ± 13.0 (3.1%)	1.4 ± 0.1 (7.0%)
Mean ± S.E.M.		130.2 ± 22.0	739.5 ± 440.6	1.3 ± 0.04
CYP2B6	MM^1-b	155.8 ± 18.2 (11.7%)	14.1 ± 0.6^1-c (4.6%)	NA^1-d

Rates of HBUP formation were determined in duplicate at 10 to 2000 μM BUP in HLMs 13, 14, 16, 17, and 25 and in CYP2B6-containing insect cell-derived microsomes. Weighted concentration-rate data were fit to the Hill equation (HLMs 13, 14, 16, 17, and 25) or to a one-component Michaelis-Menten model (cDNA-expressed 2B6) by nonlinear regression using the WinNonlin program. Kinetic parameters were estimated from the fitted data.

↵1-a Parameter estimate ± S.E. of parameter estimate; values in parentheses represent coefficients of variation of parameter estimates.
↵1-b MM, Michaelis-Menten.
↵1-c V_max expressed as pmol/min/pmol of P450.
↵1-d NA, not applicable.