Abstract
The reduction of both the membrane bound, rat liver microsomal and the soluble, bacterial cytochromes P-450 by sodium dithionite has been studied as a function of temperature (4–37°) and reductant concentration. The results indicate that in this temperature range (a) the reduction of the microsomal enzyme is a biphasic process; each phase is first order at a given dithionite concentration and the percentage of slower phase is relatively constant (70–80%) and independent of the presence or absence of exogenous substrate; (b) the reduction of cytochrome P-450cam is a first order process throughout the temperature range employed and independent of the presence or absence of d-camphor; (c) neither the fast or slow phase of reduction of microsomal cytochrome P-450 nor the single phase of cytochrome P-450cam reduction exhibits a break in the Arrhenius plot; (d) the presence of substrate results in a significant decrease in the rate constant for the dithionite dependent reduction; and (e) the reduction by dithionite does not appear to be a second order process. These findings are compared with previously obtained data from a study of the NADPH-dependent reduction of microsomal cytochrome P-450.
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