Cell-free extracts of Peptostreptococcus elsdenii, a strict anaerobe from the rumen, were examined for enzymes catalysing the steps in the biosynthesis from lactate of alanine, serine, aspartate and glutamate. Extracts contain the enzymes necessary for the formation of alanine from lactate via pyruvate. The presence of enzymes catalysing the interconversion of phosphoglycerate and phosphohydroxypyruvate, the transamination of the latter to phosphoserine and the cleavage of phosphoserine to serine and inorganic phosphate was demonstrated, suggesting that serine is formed via these intermediates. ‘Malic’ enzyme, malate dehydrogenase and glutamate–oxaloacetate transaminase are present in extracts and could account for aspartate formation. The extracts catalyse all of the steps of the tricarboxylic acid pathway leading from oxaloacetate plus acetate to glutamate. Together with substantive data from previous radioactive tracer studies the results provide strong evidence that these four amino acids are synthesized in this strict anaerobe by pathways closely similar to those operating in aerobic and facultatively aerobic organisms.
