Glucosamine metabolism. V. Enzymatic synthesis of glucosamine 6-phosphate.

Studies in viva on the biosynthesis of n-glucosamine, with the use of specifically labeled glucose in the rat (1,2) and in group A streptococci (3-5) showed that the glucose carbon chain was preserved during its conversion to the hexosamine. Leloir and Cardini (6, 7) noted that extracts obtained from Neurospora crassa converted glutamine and hexose phosphate to glutamic acid and a product tentatively characterized as glucosamine 6-phosphate. Owing to the presence of phosphoglucoisomerase in the extract, it was not known whether glucose 6-phosphate or fructose 6-phosphate was the acceptor of the amido group of glutamine. A preliminary report (8) indicated that such extracts could be fractionated to remove isomerase and that glucosamine 6-phosphate synthesis occurred with fructose 6-phosphate but not with glucose 6-phosphate. Satisfactory stoichiometry studies were not possible with these preparations due to their lability and to the considerable activity of contaminating glutaminase. Subsequent work in this laboratory was performed with extracts obtained from bacteria and from rat liver (9). Studies on the rat liver enzyme were first reported by Pogell and Gryder (lo), who obtained activity with both hexose phosphates. On the basis of relative activity studies and stability experiments, they concluded that glucose 6-phosphate and not fructose 6-phosphate was the active substrate in the reaction with glutamine. The present paper gives the purification procedures and properties of the enzymes from N. crassa, Escherichia coli, and rat liver. As previously noted (9) each of the preparations was found to be specific for fructose 6-phosphate. Leloir (6, 7) suggested that the enzyme be named transamidase when its hexose phosphate specificity was unknown. In view of the present results, we suggest that the enzyme be called L-glutamine-n-fructose 6-phosphate transamidase.