The role of coenzyme binding in regulating interflavin electron transfer in human cytochrome P450 reductase (CPR) has been studied using temperature-jump spectros-copy. Previous studies [Gutierrez, A., Paine, M., Wolf, ., Scrutton, ., & Roberts, (2002) 41,4626–4637] have shown that the observed rate, 1/s, of interflavin electron transfer (FADsq )FMNsq fi FADox)FMNhq) inCPRreduced at the two-electron level with NADPH is 55 ± 2 s )1 , whereas with dithionite-reduced enzyme the observed rate is 11 ± s )1 ,sug-gesting that NADPH (or NADP + ) binding has an important role in controlling the rate of internal electron transfer
