The mechanism of succinate or fumarate transfer in the tricarboxylic acid cycle allows molecular rotation of the intermediate.

TitleThe mechanism of succinate or fumarate transfer in the tricarboxylic acid cycle allows molecular rotation of the intermediate.
Publication TypeJournal Article
Year of Publication1990
AuthorsBernhard, S. A., and P. Tompa
JournalArch Biochem Biophys
Volume276
Issue1
Pagination191-8
Date Published1990 Jan
ISSN0003-9861
KeywordsAnimals, Carbon Isotopes, Citric Acid Cycle, Fumarates, Glutamates, Kinetics, Magnetic Resonance Spectroscopy, Male, Mitochondria, Liver, Rats, Rats, Inbred Strains, Succinates
Abstract

Mitochondria were incubated with L[5-13C]glutamic acid and the distribution of the label between the two carboxyl carbon atoms of the L-aspartic acid formed was determined by 13C NMR. The reaction sequence leading from L-glutamic acid to L-aspartic acid spans the tricarboxylic acid cycle reactions involving the two symmetrical intermediates succinate and fumarate. The C2 symmetry of these intermediates in principle permits a discrimination of the mechanism of their transfer between their enzyme sites of production and utilization. A direct transfer of metabolite from site to site by translation alone predicts an unequal distribution of 13C between the C1 and C4 of aspartate, whereas molecular rotation during transfer allows for a scrambling of the original C5 label. Under several conditions of different glutamate concentrations and solvent osmotic pressures, equal labeling in the C1 and C4 carbons of aspartate is observed. This observation is inconsistent with a transfer mechanism restricting molecular rotation for both intermediates but is compatible with both a random diffusion and a direct transfer mechanism provided the latter allows molecular rotation.

Alternate JournalArch. Biochem. Biophys.
PubMed ID2297223
Grant ListGM 37056 / GM / NIGMS NIH HHS / United States