Amino acid synthesis by the mitochondria of Neurospora crassa: I. Dependence on respiration of mitochondria

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The synthesis of valine, isoleucine, alanine, glutamate, and aspartate by isolated mitochondria of Neurospora crassa was markedly enhanced by the addition of ADP, inorganic phosphate, and succinate to an incubation mixture containing the precursors, pyruvate, and α-ketobutyrate. The addition of either 2,4-dinitrophenol or oligomycin to the incubation mixture caused a significant reduction in the amount of amino acids produced. KCN caused an even more marked reduction. It is concluded that the synthesis of these amino acids by the mitochondria is in part dependent on respiration and associated oxidative phosphorylation. It was shown by using 14C-labeled succinate that carbon from succinate is not incorporated into either alanine or valine, but it is into aspartate and glutamate. The relative amount of incorporation into the latter two amino acids can be varied by adding or omitting exogenous pyruvate. While exogenous pyruvate is incorporated into valine, it is also apparent that a pool of endogenous source of precursor exists which contributes significantly to valine synthesis in respiring mitochondria.