THE ACCUMULATION OF α-KETOGLUTARATE BY SUSPENSIONS OF PSEUDOMONAS AERUGINOSA

Pyruvic and α-ketoglutaric acids accumulated during the oxidation of glucose by washed cell suspensions of Pseudomonas aeruginosa harvested from a glucose medium. The addition of ammonium salts had been shown to prevent the accumulation of the α-ketoglutaric acid in such suspensions. A similar situation was shown to exist with growing cultures. The accumulation of α-ketoglutaric acid was not due to inability of the cells to synthesize enzymes required for the oxidation of this compound. Cells harvested from a glucose medium required an induction period before oxidizing α-ketoglutaric acid but this was apparently due to the lack of a permease required for the transport of the substrate across the cell membrane. A comparison of the enzyme levels of cell extracts prepared from cells grown on a glucose medium with those grown on an α-ketoglutaric acid medium revealed that the latter had a higher level of the individual apoenzymes required for α-ketoglutaric acid oxidation. However, the apoenzyme level of the extracts of glucose-grown cells appeared adequate to prevent the accumulation of α-ketoglutaric acid during glucose oxidation.It is concluded that during growth in the presence of an excess of ammonium salts α-ketoglutarate never escapes from the internal metabolic pool of the cells and therefore the permease for α-ketoglutarate is not synthesized. During glucose oxidation by washed suspensions of glucose-grown cells, α-ketoglutarate is perhaps excreted from the cell either because the cells are deficient in the coenzymes necessary for α-ketoglutarate oxidation or because the avidity of the enzymes for substrate is such that, at low levels of substrate, the enzymes of α-ketoglutarate oxidation act so slowly that the intermediate accumulates.