Cytochrome b5 as electron donor to rabbit liver cytochrome P-450LM2 in reconstituted phospholipid vesicles

When incorporated into phospholipid vesicles containing NADPH-cytochrome P-450 reductase and P-450_LM2, cytochrome b₅ enhanced the rate of NADPH-supported hydroxylation of 7-ethoxycoumarin or $\text{p}$-nitroanisole about 5-fold. Cytochrome b₅ did not affect the rate of NADPH-oxidation, nor the rate of NADPH-supported formation of the ferrous CO-complex of cytochrome P-450. However, the cytochrome b₅-mediated increase in product formation was found to be correlated with concomitant decreases in the production of H₂O₂ or $\text{O}{}_2{}^{\mathrm{?}}$ in the system, thus strongly indicating cytochrome b₅ being a more efficient donor of the second electron to cytochrome P-450 than is NADPH-cytochrome P-450 reductase.