The biosynthesis of aspartic acid, glutamic acid, and alanine in Rhizobium japonicum

Abstract

The biosynthesis of aspartic acid and the incorporation of its carbon skeleton into glutamic acid and alanine was investigated in Rhizobium japonicum. It was found that oxalacetic acid (OAA) occupies a key position in the metabolism of this amino acid and the dissemination of its carbon skeleton into other amino acids. Aspartic acid is formed by two pathways involving the amination of OAA. In one pathway, OAA is synthesized by the tricarboxylic acid (TCA) cycle and in the other by the carboxylation of either pyruvate or phosphoenolpyruvate. The carbon skeleton of aspartic acid can be incorporated into alanine either by deamination to OAA followed by decarboxylation to pyruvate and reamination or directly by decarboxylation of the number four carbon. There are at least two pathways by which aspartic acid carbon is incorporated into glutamic acid. One path involves the synthesis of α-ketoglutarate from OAA via the TCA cycle, the other is a condensation yielding either β-methylaspartate or α-ketoglutarate, which is then converted to glutamate.