Intracellular pH effect upon phosphoglucose isomerase in Escherichia coli

Abstract

Abstract 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 32 P-labelled orthophosphate, strongly suggests that E. coli contains an active mannitol kinase.