Isomerase Activity of the C-terminal Fructose-6-phosphate Binding Domain of Glucosamine-6-phosphate Synthase from Escherichia coli

The isomerase activity of the C-terminal fructose-6P binding domain (residues 241–608) of glucosamine-6-phosphate synthase from Escherichia coli has been studied. The equilibrium constant of the C-terminal domain keq ([glucose-6P]/[fructose-6-P]) = 5.0. A noncompetitive product inhibition of the isomerase activity by the reaction product glucose-6-P has been detected. The existence of more than one binding and reaction sites for the substrate fructose-6P on the molecule of glucosamine-6-phosphate synthase can be expected. The fructose-6P binding domain possibly includes a regulatory site, different from the catalytic center of the enzyme.