Studies on l-Glutamine d-Fructose 6-Phosphate Amidotransferase

The enzyme, l-glutamine d-fructose 6-phosphate amidotransferase (EC 2.6.1.16), that catalyzes the formation of glucosamine 6-phosphate has been partially purified from rat liver, HeLa cells, Escherichia coli, and Bacillus subtilis. Enzyme from the mammalian sources is subject to feedback inhibition by uridine diphosphate-N-acetyl-d-glucosamine, but enzyme from the bacteria is not. The approximate molecular weights, estimated by sucrose density gradient centrifugation, are 340,000 for enzyme from the former two sources, and 100,000 for enzyme from the latter two. Kinetic studies on the rat liver enzyme show that UDP-N-acetyl-d-glucosamine increases the Michaelis constant (Km) for fructose 6-phosphate without affecting the maximum velocity, and that it does not alter the Km for l-glutamine. A variety of treatments result in partial desensitization of the rat liver enzyme to inhibition by UDP-N-acetyl-d-glucosamine, suggesting that the inhibitor binds at a site on the enzyme distinct from the active site.