Binding of substrates and modifiers to glucosamine synthetase.
1. The binding of substrates and effectors to glucosamine synthetase (l-glutamine-d-fructose 6-phosphate aminotransferase, EC 2.6.1.16) was studied by using the ligand to alter the denaturation rate of the enzyme. The free enzyme bound fructose 6-phosphate, glucose 6-phosphate and UDP-N-acetylglucosamine, but not glutamine, AMP or UTP. Glucose 6-phosphate and AMP increased the binding of UDP-N-acetylglucosamine whereas UTP decreased the interaction between the enzyme and the feedback inhibitor. UDP-N-acetylglucosamine induced a glutamine-binding site on the enzyme. 2. Selective thermal or chemical denaturation revealed that the UDP-N-acetylglucosamine-binding site was not located at the catalytic site. The UTP site could not be distinguished from that for the nucleotide sugar. The AMP- and glucose 6-phosphate-binding sites were distinct from the catalytic and feedback-inhibitor-binding sites. 3. The specificity of the glutamine-binding site was investigated by using a series of potential analogues. 4. A model is proposed for the action of the effectors and the mechanism of the reaction discussed in kinetic and chemical terms.
D000494:Allosteric Regulation; D000818:Animals; D001665:Binding Sites; D002729:Chloromercuribenzoates / Q000494:pharmacology; D005636:Fructosephosphates; D005944:Glucosamine; D005958:Glucosephosphates; D005973:Glutamine; D008099:Liver / Q000201:enzymology; D008956:Models, Chemical; D011489:Protein Denaturation; D051381:Rats; D013696:Temperature; D000637:Transaminases / Q000037:antagonists & inhibitors; D014500:Uracil Nucleotides
D002729:Chloromercuribenzoates; D005636:Fructosephosphates; D005958:Glucosephosphates; D014500:Uracil Nucleotides; D005973:Glutamine; D000637:Transaminases; D005944:Glucosamine