[Xanthine oxidase activity in transplantable Guerin's carcinoma in rats].

Influence of low-dosage pre-irradiation on xanthine oxidase levels in Guerin's carcinoma was studied with particular emphasis on free oxygen generation and free sulphohydrils in a fraction of proteins characterized by xanthine oxidase activity. Enhanced growth of tumor correlated with that of xanthine oxidase activity involving higher levels of enzymatic O-form due to thiol groups oxidation. Under similar conditions, xanthine oxidase and free oxygen generation levels were higher due to SH-group oxidation than in intact animals. Terminal stages involved dropping xanthine oxidase levels and enzymatic protein degradation.