Association between the α-ketoglutarate dehydrogenase complex and succinate thiokinase

Abstract

The kinetic parameters of the individual reaction of pig heart α-ketoglutarate dehydrogenase complex, succinate thiokinase and the α-ketoglutarate dehydrogenase complex-succinate thiokinase coupled system were studied. The K m CoA of α-ketoglutarate dehydrogenase complex and the K m succinyl CoA of succinate thiokinase decreased in the coupled system when compared to those of the individual enzyme reactions. This phenomenon can be explained by the interaction between the α-ketoglutarate dehydrogenase complex and succinate thiokinase. By means of poly(ethylene glycol) precipitation, ultracentrifugation and gel chromatography we were able to detect a physical interaction between the α-ketoglutarate dehydrogenase complex and succinate thiokinase. Of the seven investigated proteins only succinate thiokinase showed associated with α-ketoglutarate dehydrogenase complex. On the other hand, succinate thiokinase did not associate with other high molecular weight mitochondrial enzymes such as pyruvate dehydrogenase complex and glutamate dehydrogenase. On this basis, the interaction between succinate thiokinase and α-ketoglutarate dehydrogenase complex was assumed to be specific. These in vitro data raise the possibility that a portion of the citric acid cycle enzymes exists as a large multienzyme complex in the mitochondrial matrix.