Inactivation of glucosamine-6-phosphate synthetase from Salmonella typhimurium LT2 by fumaroyl diaminopropanoic acid derivatives, a novel group of glutamine analogs

A novel group of glutamine analogs, N3-fumaroyl-L-2,3-diaminopropanoic acid (FDP) and its derivatives and analogs including amide (FCDP), methyl ester (FMDP) and its homologue, N4-(4-methoxyfumaroyl)-L-2,4-diaminobutanoic acid, inactivate glucosamine-6-phosphate synthetase (L-glutamine: D-fructose-6-phosphate aminotransferase (hexose-isomerizing), EC 2.6.1.16), isolated from Salmonella typhimurium, by covalent modification. For comparative purposes, selected known glutamine analogs were also examined. Anticapsin, 6-diazo-5-oxo-L-norleucine and, at high concentration, azaserine inactivate the enzyme. The pseudo-first-order rate constants show a hyperbolic dependence on inhibitor concentration for all the above-mentioned inhibitors, suggesting the formation of a reversible complex prior to covalent modification. Dissociation constants for inhibitors were determined and ranged from 10(-4) M for FCDP to 10(-6) M for FMDP. Albizziin, gamma-glutamylhydroxamate and, at low concentration, azaserine inhibit glucosamine synthetase only reversibly. All inhibitors tested are competitive in relation to glutamine. and competitive inhibitors, albizziin and gamma-glutamylhydroxamate protect the enzyme against inactivation. Fructose 6-phosphate accelerates the rate of inactivation. Some analogs of FDP, such as SMDP, CRDP, O-FMSer, MMDP and AADP, are not active against glucosamine-6-phosphate synthetase. The structure-activity relationship of the novel group of glutamine analogs is discussed and structural requirements for the activity of these compounds is established. It is postulated that the compounds examined can be classified as mechanism-based enzyme inactivators.