Existence of a New Reactive Intermediate Oxygen Species in Hypoxanthine and Xanthine Oxidase Reaction

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We investigated a hypoxanthine (HPX) and xanthine oxidase (XOD) reaction by using a luminol analog 8-amino-5-chloro-7-phenylpyrido[3,4-d]pyridazine-1,4-(2H,3H)dione sodium salt (L-012)-mediated chemiluminescence (CL) response. Addition of a high activity of superoxide dismutase (SOD), a potent O^<-・>_2 scavenger, and of a high concentration of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), a potent spin trapping agent, diminished completely the CL response. Whereas a high concentration of dimethyl sulfoxide (DMSO), as a potent ^・OH scavenger could not attain to the complete diminishment of the CL response. It has been reported that luminol monoanion reacts with ^・OH to form luminol radical, and then resultant luminol radical reacts with O^<-・>_2 to elicit CL response. Complete scavenging for ^・OH is assumed to result in lack of luminol radical, which in turn induces lack of CL response. However, our results did not support the idea. Furthermore, we examined the effect of L-012 on the DMPO-OOH formation in the presence or absence of DMSO in the HPX-XOD system by applying an electron spin resonance (ESR)-spin trapping method. The DMPO-OOH formation was inhibited even in the presence of DMSO, and the rate constant (k_2) between L-012 and O^<-・>_2 obtained in the presence of DMSO was 9.77×10^2M^<-1>S^<-1> and the constant in the absence of DMSO was 2.97×10^3M^<-1>S^<-1>. The data suggests that L-012 is converted to a radical form that reacts with O^<-・>_2 even under the conditions of the absence of ^・OH. From these, we postulate that the existence of a reactive intermediate oxygen species in the HPX-XOD system.
公益社団法人日本薬学会の論文
2008-08-01

Existence of a New Reactive Intermediate Oxygen Species in Hypoxanthine and Xanthine Oxidase Reaction

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