Effects of Water Miscible Organic Co-solvents on Enzyme Kinetic Parameters of Drug Metabolizing Enzymes in Rat Liver Microsomes

We have investigated the effects of methanol, acetonitrile, dimethyl sulphoxide or dioxane on enzyme kinetic parameters (Km and Vmax) p-nitrophenol hydroxylation, phenacetin deethylation metoprolol metabolism in rat liver microsomes, at different solvent concentrations. In case methanol (0.1 %-0.75 % v/v) (0.01 %-0.075 showed 1.3 2.5-fold increase respectively, Km with a less marked effect Vmax. contrast, %-0.75% 1.96-fold decrease Unlike, sulphoxide, acetonitrile activation hydroxylation activity as indicated by 0.7-fold Km. metabolism, resulted 1.5 to 3.1-fold all three metabolite formation pathways concentration dependent manner, Vmax reaction. Interestingly, while did not affect for 1 2 formation, 3 was decreased manner again little values. Further, had no increased 2-fold. The formations found be presence methanol. microsomes followed atypical kinetics. Methanol auto kinetics range studied. Dimethyl appeared unsuitable characterizing Cytochrome450 mediated reactions because they very significant Vmax/Km ratio, starting concentrations 0.025 v/v 0.25 v/v, respectively. <0.5 acceptable solvents solubilization substrates metabolized Cytochrome450s.