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[U13C]Glutamate metabolism in rat brain mitochondria reveals malic enzyme activity

Bakken, Inger J.1,2; Sonnewald, Ursula2,4; Clark, John B.3; Bates, Timothy E.3

Neurochemistry

13C nuclear magnetic resonance spectroscopy was used to study the activity of malic enzyme in isolated brain mitochondria from rat in the presence of unlabelled malate and [U-13C]glutamate. ADP, inorganic phosphate, malate and [U-13C]glutamate were added to a suspension of oxygenated mitochondria. Typical tricarboxylic acid (TCA) cycle constituents (malate, 2-oxoglutarate and succinate) were labelled from [U-13C]glutamate and detected in the superfusion medium. The labelling patterns in the different atom positions of glutamate revealed entry of both unlabelled and labelled acetyl-CoA into the TCA cycle. Unlabelled acetyl-CoA was derived via pyruvate from exogenously applied malate by the action of mitochondrial malic enzyme, while labelled acetyl-CoA was derived from TCA cycle intermediates, most likely by the action of mitochondrial malic enzyme on malate produced from [U-13C]glutamate. The results demonstrate malic enzyme activity and pyruvate recycling in isolated rat brain mitochondria.

1Institute of Physics, Norwegian University of Science and Technology (NTNU), Trondheim

2MR-Center, SINTEF UNIMED, N-7034 Trondheim, Norway

3Department of Neurochemistry, Institute of Neurology, University College London, UK

4Corresponding Author: Ursula Sonnewald

ACKNOWLEDGEMENTS: The authors would like to acknowledge the financial support of the Norwegian Research Council and the SINTEF-UNIMED found.

Received 3 February 1997; accepted 17 March 1997

© Lippincott-Raven Publishers.