Effect of ATP on glucose-6-phosphate isomerase from Bacillus caldotenax.

Glucose-6-phosphate isomerase (D-glucose-6-phosphate ketol-isomerase, EC 5.3.1.9) from Bacillus caldotenax exhibits negative cooperativity in enzyme activity. Fructose 1-phosphate, fructose, 1,6-bisphosphate, phosphoenolpyruvate, 6-phosphogluconate, 3-phosphoglycerate, ATP and Pi competitively inhibit the enzyme and abolish negative cooperativity in enzyme activity, while glucose 1-phosphate, dihydroxyacetone phosphate, glyceraldehyde 3-phosphate, ADP and AMP do not inhibit the enzyme. Among the inhibitors of which intracellular concentrations can be measured, only ATP inhibits the enzyme and abolishes negative cooperativity in enzyme activity at intracellular concentration. Such ATP inhibition is observed at 65 degrees C, but not at 30 degrees C, and the inhibition becomes less effective as the temperature decreases.