STOICHIOMETRY OF OXYGEN UPTAKE, NADPH OXIDATION AND ETHYLMORPHINE N-DEMETHYLATION BY HEPATIC MICROSOMES

Abstract

The initial rate of oxygen uptake is as much as 30% greater than the initial NADPH uptake. After about one minute the rates parallel each other. The lack of stoichiometry occurs in both the presence and absence of ethylmorphine. Although there is not the expected 1:1 stoichiometry between oxygen uptake and NADPH oxidation as determined by the initial rate, when known concentrations of NADPH are added there is an excellent 1:1 stoichiometry of NADPH added to oxygen consumed indicating that in the end all the oxygen goes to peroxide which in turn disproportionates to oxygen and water. The excess oxygen uptake is only minimally affected by superoxide dismutase or NADH and, in fact, the initial oxidation of NADH by itself is also significantly less than the initial oxygen uptake. Unlike NADPH, the rate of NADH oxidation and oxygen uptake are reduced by ethyl-morphine. Our data suggest formation of intramicrosomal superoxide anion radical which then disproportionates to peroxide and oxygen.