Synthesis of Amino Acids from Succinate by the Mitochondria of Neurospora crassa

Abstract

The synthesis of valine by isolated Neurospora mitochondria in the presence of pyruvate is increased more than twofold when the cofactor assay mixture consisting of NADP, thiamine pyrophosphate (TPP), glucose-6-phosphate, and pyridoxal phosphate, and the respiring assay mixture containing ADP, orthophosphate, and succinate are combined. Although no single component of the cofactor mixture is completely responsible for the increase in valine synthesis, addition of TPP to the respiring assay mixture has the greatest effect.Neurospora mitochondria are able also to synthesize valine when pyruvate and glucose-6-phosphate are omitted from the combined mixtures. The succinate, a component of the respiring mixture, is the carbon source for the synthesis of valine, alanine, and glutamic acid. However, these syntheses require the addition of succinate, NADP, and TPP only. Addition of ADP and orthophosphate has no effect on the amounts of amino acids synthesized from succinate. Provisional evidence is presented that the source of pyruvate used in such syntheses is succinate-derived malate which is then converted to pyruvate by a mitochondrial decarboxylating malate dehydrogenase ("malic" enzyme).