Inactivation of .gamma.-aminobutyric acid aminotransferase by (S,E)-4-amino-5-fluoropent-2-enoic acid and effect on the enzyme of (E)-3-(1-aminocyclopropyl)-2-propenoic acid

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Abstract
(S,E)-4-Amino-5-fluoropent-2-enoic acid (6) is synthesized in six steps starting from the known .gamma.-aminobutyric acid aminotransferase (.gamma.-Abu-T) inactivator, (S)-4-amino-5-fluoropentanoic acid (1). Compound 6 is a mechanism-based inactivator of .gamma.-Abu-T: time-dependent inactivation is saturable and protected by substrate; thiols do not protect the enzyme from inactivation; no enzyme activity returns upon dialysis. This compound (6) binds 50 times more tightly to .gamma.-Abu-T than does the saturated analogue (1). No transamination of 6 occurs prior to inactivation. However, five molecules of 6 are required to inactivate the enzyme with concomitant release of five fluoride ions. Therefore, four molecules are being converted to product for each inactivation event. (E)-3-(1-Aminocyclopropyl)-2-propenoic acid is synthesized in seven steps from 1-aminocyclopropanecarboxylic acid. It is prepared as a cyclopropyl derivative of the proposed intermediate in the activation of .gamma.-Abu-T by 6. The cyclopropyl derivative, however, is a noncompetitive inhibitor and does not inactivate the enzyme. This study shows the usefulness and hazards of incorporation of a trans double bond into potential .gamma.-Abu-T inactivators.