Irreversible inhibition of glutamate decarboxylase by alpha-(fluoromethyl)glutamic acid

alpha-(Fluoromethyl)glutamic acid (FMG) was synthesized and shown to be an active site directed irreversible inhibitor of glutamate decarboxylase (EC 4.1.1.15) from Escherichia coli. The KI for the active enantiomer is 1.4 microM, and the kinh = 5.9 X 10(-3) s-1. Substrates for the enzyme, such as L-glutamate, and competitive inhibitors, such as citrate, decrease the rates of FMG-mediated inactivation of the enzyme. A profound change in the ultraviolet spectrum of the enzyme accompanies the inactivation process. When [3H]-FMG is used, it can be shown that the enzyme incorporates radioactivity at the same rate as that of inactivation. There is a 1:1 stoichiometry of [3H]FMG incorporated to pyridoxal phosphate binding subunits of the enzyme. From these and other studies it is concluded that FMG is a substrate for the enzyme and alkylates it as a consequence of this turnover.