Study of amino acid formation during palmitate oxidation in rat brain mitochondria

The interrelation of palmitate oxidation with amino acid formation in rat brain mitochondria has been investigated in purified mitochondria of nonsynaptic origin by measuring the formation of aspartate, alpha-ketoglutarate, and glutamate during palmitate oxidation, and also by assaying 14C-products of [1-14C]palmitate oxidation. Oxidation of palmitate (or [1-14C]palmitate) resulted in the formation of aspartate (or 14C-aspartate), and the oxidation was inhibited by aminooxyacetate (an inhibitor of transaminase). Palmitate oxidation also resulted in alpha-ketoglutarate formation, which was sensitive to the effect of aminooxyacetate. Addition of NH4Cl was found to increase 14C-products and formation of alpha-ketoglutarate, whereas glutamate formation was not increased unless the rate of palmitate oxidation was reduced by 50% by aminooxyacetate or alpha-ketoglutarate was added exogenously. Exogenous alpha-ketoglutarate was found to decrease 14C-products, but not aspartate formation. These results indicated that palmitate oxidation was closely related to aspartate formation via aspartate aminotransferase. During palmitate oxidation without aminooxyacetate or added alpha-ketoglutarate, however, alpha-ketoglutarate was not available for glutamate formation via glutamate dehydrogenase. We discuss the possibility that this was because (a) oxidative decarboxylation of alpha-ketoglutarate to form succinyl-CoA was favored over glutamate formation for the competition for alpha-ketoglutarate in the same pool, and (b) the pool of alpha-ketoglutarate produced in the aspartate aminotransferase reaction did not serve as substrate for glutamate formation.