Oxygen-concentration dependence of microsomal chemiluminescence

The effect of varying concentrations of oxygen on NADPH-dependent microsomal chemiluminescence was determined. Light emission increased as the concentration of oxygen was elevated from 0 to 10 to 20%, and then began to decrease upon further increases in oxygen concentration to 50 and 100%. This biphasic response of chemiluminescence is similar to that previously observed for microsomal generation of hydroxyl radical, however, the light emission was not sensitive to superoxide dismutase, catalase or benzoate confirming the lack of a role for ·OH in the light emission. The biphasic nature of the response of chemiluminescence is similar to that reported for exhalation of ethane and pentane but not that of malondiadehyde as a measure of lipid peroxidation, although the concentrations of O₂ to reach the maximum effect differ. Activity of NADPH-cytochrome P450 reductase was decreased at the elevated concentrations of O₂. The biphasic response of chemiluminescence to O₂ appears to reflect the need for a critical amount of O₂ to generate the initiating oxidizing species, and the effect of O₂ on the appropriate redox state of the iron catalyst.