Intracellular pH effect upon phosphoglucose isomerase in Escherichia coli

• 1.

  1. Whole cells of Escherichia coli hydrolyze fructose 1,6-diphosphate to fructose 6-phosphate, and when the cells are incubated in an unbuffered medium the product is not isomerized to glucose 6-phosphate. The reason for this lack of isomerization has been investigated.

• 2.

  Ubder specified conditions phosphoglucose isomerase (d-glucose-6-phosphate ketol isomerase, EC 5.3.1.9) is inhibited, probably because of a low pH in the cells which is unfavourable for the phosphoglucose isomerase reaction, but which permits other enzymes in the glycolytic sequence to act.

• 3.

  3. Aerobically incubated cells of E. coli contain more acids than what is found under anaerobic conditions. This may result in a pH inhibition of the phosphoglucose isomerase which is dependent upon the oxygen pressure.

• 4.

  4. In suspensions of E. coli buffered at pH 5.8, hydrolysis in the 1 position is competing favourably woth glycolytic breakdown of fructose 1,6-diphosphate.

• 5.

  5. The specific radioativity of mannitol 1-phosphate observed in experiments with ³²P-labelled orthophosphate, strongly suggests that E. coli contains an active mannitol kinase.