The effect of magnesium ions on the diemthylaniline oxidation rate and electron transfer in liver microsomal fraction

Abstract

1. Reactions of N-demethylation, p-hydroxylation and N-oxidation of one substrate, i.e. dimethylaniline, have been used to show that the activating effect of Mg²⁺ takes place only in the first two reactions. 2. An increase in V_max. of N-demethylation of dimethylaniline is accompanied by an increase in K_m. In the p-hydroxylation of dimethylaniline V_max. increases whereas K_m does not change. A comparison of the changes in the K_m values of these reactions with the change in K_s shows that in both cases K_m does not characterize the affinity of cytochrome P-450 for dimethylaniline. 3. The rate-limiting site of N-demethylation and p-hydroxylation of dimethylaniline, as well as the total rate of NADPH oxidation in the presence of dimethylaniline, is between cytochromes b₅ and P-450. Addition of Mg²⁺ to the incubation medium changes the hydrophobic environment of phosphatidylcholine in the membrane, the process being accompanied by a sharp increase in the fluorescence quantum yield of 8-anilinonaphthalene-1-sulphonate.