Previous estimates of flux through the pyruvate‐dehydrogenase complex were made by measuring 14CO2 generated from oxidation of [1‐14C]pyruvate, assuming a 1:1 stoichiometry. However, this method fails to discriminate between 14CO2 produced from pyruvate dehydrogenase and 14CO2 generated from phospho‐enolpyruvate carboxykinase and citric‐acid‐cycle dehydrogenases. While some previous reports have attempted to correct for the additional 14CO2 production by comparing 14CO2 generated by [1‐14C]pyruvate with [2‐14C]pyruvate or [3‐14C]pyruvate, the estimates are flawed by failure to determine the radioactivity and distribution of the 14C label in the oxalacetate pool. The present method circumvents these problems by utilizing [1,4‐14C]succinate to radiolabel the oxalacetate pool and by directly measuring the specific radioactivity of malate. The results demonstrate that flux through the pyruvate‐dehydrogenase complex is negligible compared to the other reactions which generate 14CO2 from [1‐14C]lactate in the fasted state. Phenylephrine did not significantly alter this result in the fasted state. However, 14CO2 production via the pyruvate‐dehydrogenase complex is large (∼ 11.5 nmol · min−1· mg mitochondrial protein−1) compared to 14CO2 production via phosphoenolpyruvate carboxykinase and citric‐acid‐cycle dehydrogenases (∼ 6.4 nmol · min−1· mg−1) when the pyruvate‐dehydrogenase complex is activated, in the fed state with 1 mM dichloroacetate.
|Original language||English (US)|
|Number of pages||7|
|Journal||European Journal of Biochemistry|
|State||Published - Feb 1991|
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