INHIBITION OF GABA TRANSAMINASE ACTIVITY BY 4‐AMINOTETROLIC ACID

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Abstract
Abstract— The influence of the following acetylenic analogues of GABA on GABA‐metabolizing enzymes was studied in vitro: 4‐amino‐, 4‐morpholino‐, 4‐piperazino‐, 4‐piperidino‐ and 4‐pyrrolidinotetrolic acid. 4‐Aminotetrolic acid was a linear competitive inhibitor of GABA transaminase activity in extracts of rat cerebral mitochondria and a linear noncompetitive inhibitor of this enzyme activity in extracts of P. fluorescens when activity was measured with GABA as the variable substrate. From these results it was calculated that the dissociation constants for the binding of 4‐aminotetrolic acid to the pyridoxal form of these enzymes are approx. 1 mM. The other substituted tetrolic acids did not influence either transaminase activity under the conditions studied. None of the substituted tetrolic acids influenced the L‐glutamic acid decarboxylase activity in extracts of rat cerebral cortex and of E. coli.