Table 2. Kinetic constants for the simulated curves for 7-Ethoxyfluorocoumarin metabolism.

The experimental data for the reductase titrations of the mixed reconstituted systems (Fig 5) were simulated using (a) a model allowing only the formation of binary complexes, and (b) a model allowing the formation of CYP1A2-CYP2B4 complexes. The equilibrium and rate constants below are based on the model described in Scheme 1, which has been detailed in a previous report (31). Data fitting for the simpler model where both CYP1A2 and CYP2B4 compete for reductase (without P450-P450) complex formation utilize only the first 4 constants (K_ar, K_br, k_ar, and k_br)

	50 mM HEPES	300 mM HEPES
Kar	0.004	0.0073
kar	56	35
Kbr	0.036	0.0177
Kbr	2144	1080
Kbar	0.093	0.00255
Kbar	434	35
Krbar**	0.01	0.01
krbar*	2197	1115

^*In these simulations, the rate constant for the RBAR complex was set as the sum of the AR and BR complexes. This was done to constrain the simulations under the assumption that the quaternary complex would have a rate constant similar to the sum of the binary complexes.

^**Under the conditions of this experiment, the value for K_rbar could not be determined. Although the data were fit using these parameters, this value was not unique, and could have a range over 4 orders of magnitude without significantly affecting the values of the other rate constants.