The chemistry of xanthine oxidase. 5. Electron-spin resonance of xanthine oxidase solutions

Abstract

Xanthine oxidase solutions have been examined in the frozen state by means of electron-spin resonance. "Active" and "inactive" samples of xanthine oxidase were used and measurements were made both on the resting enzyme and after treatment with either xanthine or sodium dithionite. Electron-spin resonance signals consisted of 2 separate peaks. Under various conditions these peaks could be obtained alone or in combination with each other. It is concluded that the Fe of the enzyme is always in the Fe++ state, and that the Mo is reduced and free radicals are formed when the substrate is added to the active enzyme.