Inactivation of gamma-aminobutyric acid aminotransferase by L-3-chloroalanine hydroxamate.
The mechanism of inactivation of gamma-aminobutyric acid aminotransferase (GABA-AT) by L-3-chloroalanine hydroxamate (1) was investigated. Inactivation of [3H]PLP-reconstituted GABA-AT with 1 followed by denaturation gave no PMP or enamine adduct to the PLP; however, a new unknown metabolite was observed which was identical to the metabolite formed upon inactivation of GABA-AT by L-cycloserine. Time-dependent inactivation occurs, but the kinetics are second order; the rate of inactivation increases with time. After inactivation occurs the addition of fresh enzyme results in a faster rate of inactivation than prior to the initial inactivation. This indicates that the actual inactivator is generated from L-3-chloroalanine hydroxamate, and is not L-3-chloroalanine hydroxamate itself. Added gabaculine-inactivated enzyme to fresh enzyme does not increase the rate of inactivation, suggesting that the conversion of L-3-chloroalanine hydroxamate to the active form is not catalyzed by peripheral amino acid residues. L-3-Chloroalanine hydroxamate was shown to undergo buffer-catalyzed cyclization to L-cycloserine, which is the actual inactivator of GABA-AT.
Silverman
R B
RB
Department of Chemistry, Northwestern University, Evanston, IL 60208-3113, USA.
Olson
G T
GT
D000612:4-Aminobutyrate Transaminase / Q000037:antagonists & inhibitors*; D000409:Alanine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D002021:Buffers; D003509:Cyclohexanecarboxylic Acids / Q000494:pharmacology; D003523:Cycloserine / Q000494:pharmacology; D003903:Deuterium; D011355:Prodrugs / Q000494:pharmacology; D011732:Pyridoxal Phosphate / Q000737:chemistry; D013552:Swine; D013997:Time Factors
D002021:Buffers; D003509:Cyclohexanecarboxylic Acids; D011355:Prodrugs; C012721:1-alpha-amino-beta-chloropropionic acid hydroxamide; C012987:gabaculine; D011732:Pyridoxal Phosphate; D003523:Cycloserine; D003903:Deuterium; D000612:4-Aminobutyrate Transaminase; D000409:Alanine