Photo-oxidation of L-glutamate decarboxylase from Escherichia coli, sensitized by the coenzyme pyridoxal phosphate and by proflavin

Abstract

Irradiation of L-glutamate decarboxylase (L-glutamate 1-carboxy-lyase, EC 4.1.1.15) from Escherichia coli by visible light absorbed by the intrinsic chromophore, pyridoxal phosphate, caused the selective modification of two methionines per enzyme monomer. The disulfoxide derivative exhibited modified circular dichroism, chromatographic and kinetic properties, suggesting a conformational role for the two methionine residues. Irradiation of the enzyme in the presence of proflavin revealed the presence of two distinct groups of tryptophan residues with markedly different photooxidation rate constants. No evidence of involvement of tryptophans in the catalytic mechanisms of the enzyme was obtained. The results are compared with those obtained on irradiation of L-glutamate decarboxylase from Clostridium perfringens.