Table 2. K_m’s and k_cat’s determined for CYP2B4 WT and its variants and CPR.

2B4	Km (µM)	kcat (min−1)
WT	0.14±0.022	37±1.5
C79SC152S	0.19±0.023	48±1.7
C79S	0.18±0.025	41±1.6
(E60C)	0.14±0.019	54±1.9
(H226C)	0.20±0.036	41±2.3
(Y484C)	0.10±0.024	42±2.1
(V267C)	0.43±0.10	34±3.1
(R133C)	0.65±0.11	4.7±0.40
(L270C)	0.69±0.12	30±2.5
(L420C)	0.19±0.064	54±5.2

As described under “Experimental Procedures”, the kinetic parameters were determined by measuring the rate of formaldehyde formation as a result of CYP2B4-mediated N-demethylation of benzphetamine under fixed concentrations of CYP2B4 and excess benzphetamine with increasing concentrations of CPR.