Xanthine oxidase/dehydrogenase activity in intact cultured cells (in situ analysis)

The measured ratio of xanthine oxidase activity to the total activity of xanthine oxidase and dehydrogenase showed higher values in intact cells than when similar cells were homogenized. The total activity was the same for both systems. The xanthine oxidase ratio was 90, 60, 50, 50, 60% in V79, RIF/Ha3, SCC7, KHT intact cells and freshly extracted murine peritoneal macrophages respectively while the corresponding ratios measured were 25, 40, 38, 35, 22% when the cells were lysed by homogenization. Superoxide radical O2-. production by addition of xanthine to intact or homogenized cells to activate intracellular xanthine oxidase was higher in intact than homogenized cells. Homogenization of cells and tissues in the presence of dithioerythritol (DTE) can evidently lead to a considerable under-estimation of the xanthine oxidase ratio. The effect of hypoxia on cells has also been examined.