Effect of tolbutamide on the intracellular flow of acetyl coenzyme A in Tetrahymena.

Experiments were done in which control cells and cells exposed to tolbutamide for 17 hours were incubated for 1 hour with labeled pyruvate, acetate, and octanoate, and the amount of label appearing in COZ, glycogen, lipids, and glutamate was measured. In separate experiments ATP and ADP levels were also measured in control and tolbutamide-treated cells. The results of the multiple label experiments were interpreted in accordance with a previously developed model of the metabolism of Tefrahymena which has three pools of acetyl-CoA. It was found that in log phase cells there were significant increases in octanoate oxidation in the peroxisomal and inner mitochondrial pools of acetylCoA, and a shift of acetate utilization away from the peroxisome and into the inner mitochondrial compartment. Incorporation of label from [I-Wlacetate into glutamate was reduced by tolbutamide. Carbon flow from the peroxisomes for glyconeogenesis was markedly reduced, but carbon flow for glyconeogenesis from the outer mitochondrial pool was increased. In transition phase cells, however, carbon flow toward glyconeogenesis was reduced from both the peroxisomes and the mitochondria. The cell content of ATP was increased by exposure of the cells to tolbutamide; the increase was more pronounced in log phase cells. It is suggested that tolbutamide does not uncouple oxidative phosphorylation in Tefrahymena but instead alters the intracellular pattern of carbon flow because of an effect on the rate of flow of substrates across the inner mitochondrial membrane.