Inhibition by fructose 1,6-bisphosphate of transaldolase from Escherichia coli

The effect of fructose 1,6-bisphosphate (Fru 1,6-P-2) on the regulatory enzymes of pentose phosphate pathway of Escherichia coli was examined. Fru 1,6-P-2 inhibited E. coli transaldolase (EC 2.2.1.2) competitively against fructose 6-phosphate and uncompetitively against erythrose 4-phosphate, whereas Fru 1,6-P-2 did not affect glucose 6-phosphate dehydrogenase (EC 1.1.1.49) and 6-phosphogluconate dehydrogenase (EC 1.1.1.44). Kinetic results can be explained by assuming that transaldolase has two kinds of binding sites for Fru 1,6-P-2: a competitive binding site for fructose 6-phosphate and a second binding site on the enzyme-erythrose 4-phosphate complex. Fru 1,6-P-2 increased resulting from the stimulation of glycolysis, can inhibit transaldolase and further participates in the elevation of the concentration of ribose 5-phosphate that can be preferentially utilized for anabolic reaction in exponential phase of E. coli.