The one-electron reduction potential of several substrates can be related to their reduction rates by cytochrome P-450 reductase.

The rates of reduction of 27 compounds by purified cytochrome P-450 reductase have been studied and correlated with the one-electron reduction potentials E7(X/X.-). For compounds with reduction potentials between approx. -400 and -165 mV, there was a good correlation between the rates and E7(X/X.-); log rate (mumol/min per mg) = (2.38 +/- 0.08) + (0.0061 +/- 0.0003)E7 (mV). Compounds with potentials more positive than -165 mV were shown to deviate from the correlation. It is shown that under the standard conditions of the assay, these compounds undergo two-electron reduction by NADPH rather than one-electron reduction with the enzyme. As a consequence of the study, the rate constants for the reaction of superoxide radicals with native and acetylated cytochrome c were also determined to be (4.5 +/- 0.5).10(5) and (1.5 +/- 0.15).10(5) M-1 s-1, respectively.