GLYCEROLPHOSPHATE OXIDOREDUCTASES AND GLYCEROPHOSPHATE CYCLE IN EHRLICH ASCITES TUMOR CELLS

Different strains of the Ehrlich ascites carcinoma were found to differ considerably in glycerophosphate dehydrogenase (l-glycerol-3 phosphate:NAD oxidoreductase, EC 1.1.1.8) activity. Generally the activity of this enzyme amounted to 42-71 μmoles/hr/mg protein, but it was also found to approach zero. In the latter case the α-glycerophosphate cycle (GP cycle) would not be able to operate with sufficient capacity, while in the other strains the existence of low GP cycle activities was observed. Addition of NADH to the incubation medium, and elevation of the cellular triose phosphate level by the addition of glucose + iodoacetate stimulated the GP cycle. However, the increase in oxygen consumption induced by glucose and iodoacetate in the absence of external NADH could not be accounted for by an increased metabolization of glycolytically generated NADH via the GP cycle. Activities of glycerophosphate oxidase (l-glycerol-3 phosphate:cytochrome c oxidoreductase EC 1.1.2.1) were in the range 0.27-0.55 μmoles/hr/mg mitochondrial protein. Administration of triiodothyronine to the tumor mice resulted in a significant elevation of the glycerophosphate oxidase activity of the tumor mitochondria. Concomitant with this elevation, a slight stimulation of NADH metabolization via the glycerophosphate cycle was observed. © 1969.