Sl. Bearne et R. Wolfenden, GLUTAMATE GAMMA-SEMIALDEHYDE AS A NATURAL TRANSITION-STATE ANALOG INHIBITOR OF ESCHERICHIA-COLI GLUCOSAMINE-6-PHOSPHATE SYNTHASE, Biochemistry, 34(36), 1995, pp. 11515-11520
Pyrroline-5-carboxylate, an intermediate in the biosynthesis and degra
dation of glutamate, proline, and ornithine, acts as a strong reversib
le inhibitor of glucosamine-6-phosphate synthase, competitive with res
pect to glutamine. Proton magnetic resonance spectroscopy shows that,
under these conditions, pyrroline-5-carboxylate exists in rapid equili
brium with glutamate gamma-semialdehyde (0.05%). The observed variatio
n of K-i with pH is consistent with inhibition by this rare species. G
lutamate gamma-semialdehyde is expected to react reversibly with a cys
teine residue at the active site, identified by earlier inactivation s
tudies, 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.