The effect of NADH and low oxygen pressure on the hepatic microsomal ethylmorphine N-demethylase activity of the male rat.

Plots of reciprocal initial rate of formaldehyde formation as a function of reciprocal ethylmorphine concentration provide parallel lines for oxygen concentrations ranging from 5.41 to 211 microM, and the apparent Km values for ethylmorphine at these extremes are 167 and 417 microM, respectively. Similarly, the apparent Km for O2 decreases from 7.69 microM at 2 mM ethylmorphine to 3.64 microM at 0.2 mM ethylmorphine. Reciprocal plots of 1/Km app and 1/Vm for ethylmorphine against 1/[O2] give Km values for O2 of 9.35 microM and 9.09 microM, respectively. Similar plots give Km values for ethylmorphine of 0.28 mM and 0.36 mM. Similarly, NADH causes an uncompetitive stimulation. These data suggest that hepatic microsomal ethylmorphine N-demethylase follows parallel plot sequential kinetics. These results, along with studies of other workers, suggest that cytochrome P-450 forms an active complex with O2 which is stable for at least many milliseconds.