Demonstration of physical interactions between consecutive enzymes of the citric acid cycle and of the aspartate malate shuttle a study involving fumarase ec malate dehydrogenase ec citrate synthase ec and aspartate amino transferase ec

Beeckmans, S.; Kanarek, L.

European Journal of Biochemistry 117(3): 527-536


ISSN/ISBN: 0014-2956
Accession: 005104168

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By means of covalently immobilized fumarase and mitochondrial or cytoplasmic malate dehydrogenase, the physical interactions between different enzymes of the citric acid cycle (fumarase with malate dehydrogenase, malate dehydrogenase with citrate synthase and fumarase with citrate synthase) and between the enzymes of both mitochondrial and cytoplasmic halves of the aspartate-malate shuttle (aspartate aminotransferase and malate dehydrogenase) were detected. The interactions between fumarase and malate dehydrogenase were investigated by immobilizing 1 enzyme indirectly through antibodies bound to Sepharose-protein A. These results are consistent with a model in which maximally 4 molecules of malate dehydrogenase are bound to 1 fumarase molecule. This complex is able to bind either citrate synthase or aspartate aminotransferase. Apparently these enzymes bind alternatively, in order to allow the cell to perform citric acid cycle or shuttle reactions, according to its needs. The physiological meaning and implications on the regulation of metabolism of the existence of a large citric acid cycle/malate-aspartate shuttle multienzyme complex are discussed.