Interaction between citrate synthase and mitochondrial malate dehydrogenase in the presence of polyethylene glycol

Abstract

Pig heart citrate synthase and mitochondrial malate dehydrogenase interact in polyethylene glycol solutions as indicated by increased solution turbidity. A large percentage of both enzymes sediments when mixtures of the two in polyethylene glycol are centrifuged, whereas little if any of either enzyme sediments in the absence of the other. The observed interaction is highly specific in that neither cytosolic malate dehydrogenase nor nine other proteins showed evidence of specific interaction with either pig heart citrate synthase or mitochondrial malate dehydrogenase. Escherichia coli citrate synthase did not interact with pig heart citrate synthase, but did show evidence of interaction with pig heart mitochondrial malate dehydrogenase. The relation between enzyme behavior in polyethylene glycol solution and in the mitochondrion and the significance of possible in vivo interactions between citrate synthase and mitochondrial malate dehydrogenase are discussed.