Phosphoenolpyruvate carboxylation and aspartate synthesis in Acetobacter suboxydans

Dialyzed extracts of Acetobacter suboxydans ATCC 621 catalyze 14 CO 2 assimilation in the presence of phosphoenolpyruvate and a divalent cation. The formation of 14 C-oxalacetate was demonstrated and found not to be dependent upon the presence of orthophosphate or diphosphonucleotides. Oxalacetate synthesis was stimulated by orthophosphate and inhibited by aspartate. All attempts to demonstrate a reversible carboxylation mechanism have failed. 14 C-aspartate was synthesized when phosphoenolpyruvate, H 14 Co 3 − , pyridoxal phosphate, and glutamate were added to dialyzed extracts. Chromatographic and spectrophotometric analyses and chemical degradation further demonstrate the presence of a reversible aspartate aminotransferase. The function of oxalacetate synthesis in a bacterium that reportedly lacks an operative tricarboxylic acid cycle is discussed.