Substituted 4-aminobutanoic acids. Substrates for gamma-aminobutyric acid alpha-ketoglutaric acid aminotransferase.

Substituted 4-aminobutanoic acids were studied as potential irreversible inactivators of purified pig brain gamma-aminobutyric acid aminotransferase, the enzyme responsible for the degradation of the inhibitory neurotransmitter, gamma-aminobutyric acid. It was found that unlike the related 4-amino-5-halopentanoic acids (Silverman, R. B., and Levy, M. A. (1981) Biochemistry 20, 1197), the 4-amino-3-halobutanoic acids were substrates for this enzyme, undergoing exclusive elimination to succinic semialdehyde and producing no inactivation. The hydroxy analogue, however, underwent exclusive transamination and no succinic semialdehyde was detected. These results are discussed in terms of the nature of the substituents, the structure of the active site of gamma-aminobutyric acid aminotransferase, and the design of mechanism-based inactivators.