The effect of 2-oxoglutarate or 3-hydroxybutyrate on pyruvate dehydrogenase complex in isolated cerebrocortical...

The oxidation of pyruvate is mediated by the pyruvate dehydrogenase complex (PDHC; EC 1.2.4.1, EC 2.3.1.12 and EC 1.6.4.3) whose catalytic activity is influenced by phosphorylation and by product inhibition. 2-Oxoglutarate and 3-hydroxybutyrate are readily utilized by brain mitochondria and inhibit pyruvate oxidation. To further elucidate the regulatory behavior of brain PDHC, the effects of 2-oxoglutarate and 3-hydroxybutyrate on the flux of PDHC (as determined by [1-14C]pyruvate decarboxylation) and the activation (phosphorylation) state of PDHC were determined in isolated, non-synaptic cerebro-cortical mitochondria in the presence or absence of added adenine nucleotides (ADP or ATP). [1-14C]Pyruvate decarboxylation by these mitochondria is consistently depressed by either 3-hydroxybutyrate or 2-oxoglutarate in the presence of ADP when mitochondrial respiration is stimulated. In the presence of exogenous ADP, 3-hydroxybutyrate inhibits pyruvate oxidation mainly through the phosphorylation of PDHC, since the reduction of the PDHC flux parallels the depression of PDHC activation state under these conditions. On the other hand, in addition to the phosphorylation of PDHC, 2-oxoglutarate may also regulate pyruvate oxidation by product inhibition of PDHC in the presence of 0.5 mM pyruvate plus ADP or 5 mM pyruvate alone. This conclusion is based upon the observation that 2-oxoglutarate inhibits [1-14C]pyruvate decarboxylation to a much greater extent than that predicted from the PDHC activation state (i.e. catalytic capacity) alone. In conjunction with the results from our previous study (Lai, J. C. K. and Sheu, K.-F. R. (1985) J. Neurochem. 45, 1861-1868), the data of the present study are consistent with the notion that the relative importance of the various mechanisms that regulate brain and peripheral tissue PDHCs shows interesting differences.