Oxene Donors Yield Low‐Level Chemiluminescence with Microsomes and Isolated Cytochrome P‐450

Abstract

Microsomes supplemented with different oxene donors yield light emission. The ability of oxene donors to support monooxygenation paralleled the observed chemiluminescence intensities, and the following order was observed: iodosobenzene > cumene hydroperoxide > t‐butyl hydroperoxide > H2O2. Pyridine‐N‐oxide, which was reported to be effective in the bacterial camphor monooxygenase, showed neither O‐dealkylation of ethoxycoumarin nor chemiluminescence activity. Iodosobenzene‐induced chemiluminescence was not associated with high malondialdehyde accumulation, at variance with t‐butyl hydroperoxide, the lower light emission intensity of which was largely accompanied by lipid peroxidation, predominantly in a second phase of chemiluminescence. The ratio of maximal malondial‐dehyde formed/maximal chemiluminescence intensity was 30‐fold higher for t‐butyl hydroperoxide than for iodosobenzene. Low‐level chemiluminescence elicited by iodosobenzene was identified spectrally to be due, at least in part, to singlet oxygen, because of similar photoemission intensities at 634 nm and 703 nm (singlet oxygen dimol emission) and low intensity at 668 nm. Reducing equivalents to cytochrome P‐450, NADPH or NADH, exerted an inhibitory effect on iodosobenzene‐induced chemiluminescence. Aminopyrine, a substrate for microsomal monooxyganases, inhibited chemiluminescence, probably by favoring hydroxylation. Oxene donor‐supplemented isolated cytochrome P‐450 yielded low‐level chemiluminescence and the order of efficiency of the oxene donors mirrored that observed with intact microsomes. The fact that microsomes and ferricytochrome P‐450 supplemented with oxene donors yield chemiluminescence (identified partly as singlet oxygen dimol emission) is discussed in terms of heterolytic versus homolytic cleavage of the O‐O bond of hydroperoxides. Copyright © 1983, Wiley Blackwell. All rights reserved