Characterization of a Phosphoglucose Isoraerase-like Activity Associated with the Carboxy-Terminal Domain of Escherichia coli Glucosamine-6-phosphate Synthase

摘要

Glucosamine-6-phosphate (-6P) synthase (GlmS), the key enzyme for hexosamine biosynthesis, catalyzes the conversion of L-glutamine and D-fruetose-6P into glutamate and glu-cosamine-6P. The latter compound is believed to result from isomerization of fructosimine-6P generated by transimination of the Schiff base formed between the substrate and the enzyme by the amide nitrogen of glutamine. While the hydrolysis of this amide bond is characteristic of all glutamine-dependent amidotransferases and the pro-R stereospecificity of H_1 proton abstraction is the signature of all 2R-keto/aldose isomerases, the mechanism of nitrogen migration has not been elucidated. We describe here the characterization in native GlmS of a new glucose-6P synthase activity [phosphoglucose isomerase (PGI)-like activity], which was associated with the isolated earboxy-terminal domain of the protein.