Abstract
Abstract We investigated the hypoxanthine (HPX)–xanthine oxidase (XOD) reaction by examining the chemiluminescence (CL) response mediated by a luminol analog, 8-amino-5-chloro-7-phenylpyrido[3,4-d]pyridazine-1,4-(2H,3H)-dione sodium salt (L-012). It was found that addition of a high concentration of dimethyl sulfoxide (DMSO), a potent •OH scavenger, could not completely reduce the CL response. This result suggests the existence of an unknown reactive oxygen intermediate other than O2−• and •OH. We further examined the HPX–XOD reaction and the nicotinamide adenine dinucleotide phosphate (NADPH) oxidation reaction by applying an electron spin resonance (ESR) spin-trapping method. In both reaction systems, similar responses were observed. That is, addition of DMSO increased the formation of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) –OOH in a concentration-dependent manner. This indicates that scavenging of •OH increases the detected O2−• level, further suggesting the existence of an intermediate oxygen species derived from O2−• and •OH. One candidate for this species is HOOOH, presumably formed in the following way. O2−• + H+ + •OH →HOOOH
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