Observations on the enzymatic degradation and conversion of certain L-and D-amino acids by an effective strain of Rhizobium meliloti.

Abstract

Washed intact cells of an effective strain of Rhizobium meliloti oxidatively deaminated glycine and the L- and D-isomers of a number of amino acids. The interpretation of the data concerning ammonia recovery was complicated, however, by the probable occurrence of transamination and assimilation. Glyoxylic acid, produced by removal of the glycine amino group, was isolated as the corresponding dinitrophenylhydrazone. No anaerobic decarboxylation of glutamic acid or histidine was observed. Cell-free extracts synthesized glutamic acid from α-ketoglutaric acid when glycine, L-histidine, D-aspartic acid, or D-valine acted as amino-group donors. In addition, acetone-dried cells formed alanine from D-aspartic acid and pyruvate. Alanine racemase activity was detected in cell-free extracts and acetone-dried cells, but racemization of aspartic or glutamic acids did not occur. L-glutamic acid, formed by cell-free extracts in mixtures containing D-aspartic and α-ketoglutaric acids, may have been produced by a series of three coupled reactions involving racemization and L-and D-amino acid transamination.