Table 2. Kinetic constants of the simulated curves for reductase-CYP1A2-CYP2E1 reconstituted systems.

The experimental data for the reductase titrations of the mixed reconstituted systems (Fig 6) were simulated using (a) a model allowing only the formation of binary complexes, and (b) a model allowing the formation of CYP1A2-CYP2E1 complexes (see Supporting Information). The equilibrium and rate constants are based on the model described in Scheme 1, which has been detailed in a previous report (21). Data fitting for the simpler model where both CYP1A2 and CYP2E1 compete for reductase (without P450-P450) complex formation utilize only the first 4 constants (K_ar, K_br, k_ar, and k_br). ‘A’ and ‘B’ represent CYP1A2 and CYP2E1, respectively

	50 mM HEPES/ 50 mM potassium acetate	50 mM HEPES/ 300 mM potassium acetate
Kar	0.011	0.0030
Kar	414	325
Kbr	0.00013	0.012
Kbr	97	150
Kbar	0.000011	0.00033
Kbar	414	284
Krbar**	0.005	0.005
krbar*	511	465

^*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.