Enzymes of the conversion of succinate to glutamate in extracts of rumen microorganisms.

Abstract

Cell-free extracts of mixed rumen microorganisms were incubated in vitro in order to determine the existence and nature of metabolic conversions leading from succinate to glutamate. When succinate was incubated as the substrate in the presence of reduced ferredoxin (FDH), a product was formed, which reacted with 2,4-dinitrophenylhydrazine to give the hydrazone of succinic semialdehyde as determined by paper chromatography. When succinic semialdehyde was incubated in the presence of FDH and 14C-bicarbonate, fixation of label was catalyzed by the extracts. The labelled product was isolated as an organic acid and identified as 2-hydroxyglutaric acid by means of paper chromatography. In the presence of ammonia and NAD, 2-hydroxyglutarate was aminated to a ninhydrin-reactive compound that was identified as glutamate by paper chromatography.From the information obtained, a new pathway for the synthesis of glutamate in rumen microbes was proposed. This pathway entails the reduction of succinate to succinic semialdehyde, followed by reductive carboxylation of succinic semialdehyde to yield 2-hydroxyglutarate, which is then aminated to glutamate. The pathway would agree with the labelling pattern in glutamate produced in the presence of 14C-bicarbonate by mixed rumen microorganisms.