Quantitative determination of the superoxide radicals in the xanthine oxidase reaction by measurement of the electron spin resonance signal of the superoxide radical spin adduct of 5,5-dimethyl-1-pyrroline-1-oxide.

Reactivities of biologically active compounds with superoxide radicals were examined by measurement of electron spin resonance (ESR) spectra of 5-hydroperoxy-2,2-dimethyl-1-pyrrolidinyloxyl formed from 5,5-dimethyl-1-pyrroline-1-oxide and the superoxide radicals generated by xanthine-xanthine oxidase system. Quantitative determination of the superoxide radicals was performed by comparing the intensity of the spin adducts with that of 4-hydroxy-2,2,6,6-tetramethyl-pipperidinooxyl whose spin concentration was determined. Methyl viologen enhanced the formation of this spin adducts, while, rutin and luteoskyrin prevented it.