[Substrate specificity of E. coli glutamate decarboxylase].

Interaction of highly purified E. coli glutamate decarboxylase with a number substrate analogs was studied. Decarboxylation of the following amino acids was demonstrated: gamma-methylene glutamate, threo-beta-hydroxyglutamate, allo-gamma-hydroxyglutamate, threo-beta-methylglutamate, homocysteate, aminoadipate and cysteinesulfinate. The Km and either Ki or I50 values were determined for these compounds. The final products of the interaction of glutamate decarboxylase with these analogs have the same absorption spectra and capacity for reactivation by pyridoxal-P, as has the pyridoxamine-P form of the enzyme. Thus, decarboxylation of all the amino acids, mentioned above, was probably associated with the side reaction of transamination to coenzyme in the active center. Binding of aliphatic dicarboxylic acids or of valeric acid by glutamate decarboxylase leads to a slight shift of absorption spectra and of circular dichroism spectra from 420 to 423--425 nm. The following compounds fail to be bound and decarboxylated by the enzyme: gamma-aminobutyrate, D-glutamate, L-glutamine, 3,3-dimethylglutarate, methioninesulfone, methioninesulfoxide, norvaline, gamma-hydroxy-gamma-methylglutamate, erytro-beta-methylglutamate and erythro-beta-hydroxyglutamate.