Kinetics of inactivation of glutamate decarboxylase by cysteine-specific reagents

Mercuric chloride, p-chloromercuribenzoate and 5,5'-dithiobis(2-nitrobenzoic acid) irreversibly inhibited the activity of Escherichia coli glutamate decarboxylase. Their second order rate constants for inactivation are 0.463 microM(-1) min(-1), 0.034 microM(-1) min(-1), 0.018 microM(-1) min(-1), respectively. The characteristics of the inhibition by the three thiol-group reagents supports the idea that cysteinyl residues at the binding sites for the cofactor and/or the substrate are important for enzyme activity in E. coli.