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

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Abstract

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 mol/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) · 105and (1.5 ± 0.15) · 105M−1s−1, respectively.

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