GLUTAMATE GAMMA-SEMIALDEHYDE AS A NATURAL TRANSITION-STATE ANALOG INHIBITOR OF ESCHERICHIA-COLI GLUCOSAMINE-6-PHOSPHATE SYNTHASE

Pyrroline-5-carboxylate, an intermediate in the biosynthesis and degradation of glutamate, proline, and ornithine, acts as a strong reversible inhibitor of glucosamine-6-phosphate synthase, competitive with respect to glutamine. Proton magnetic resonance spectroscopy shows that, under these conditions, pyrroline-5-carboxylate exists in rapid equilibrium with glutamate gamma-semialdehyde (0.05%). The observed variation of K-i with pH is consistent with inhibition by this rare species. Glutamate gamma-semialdehyde is expected to react reversibly with a cysteine residue at the active site, identified by earlier inactivation studies, to form an analogue of a tetrahedral intermediate in glutamine hydrolysis. The apparent K-i value of glutamate gamma-semialdehyde is approximately 3 x 10(-8) M.