Kinetic studies on reduction of cytochromes P‐450 and b5 by dithionite

The kinetics of reduction of cytochromes P‐450 and b5 by dithionite had been studied in solution and in microsomal and proteoliposomal membranes by the stopped‐flow technique. In all the cases studied the kinetic curves of reduction of cytochrome b5 obey first‐order kinetics in relation to cytochrome with the rate constant about 14s−1 at 10.6 mM dithionite. The kinetic curves of reduction of cytochrome P‐450 fit an equation for the sum of two exponentials with the parameters varying from system to system. The simple first‐order kinetics of cytochrome P‐450 reduction had been observed in the presence of non‐ionic detergent Triton N‐101. The apparent biphasity of cytochrome P‐450 reduction by dithionite should be the result asymmetric distribution of hemoprotein in microsomal and proteoliposomal membranes as well as in cytochrome oligomers in solution.