G. Tunnicliff et Gj. Crites, CHEMICAL INACTIVATION OF BACTERIAL GABA AMINOTRANSFERASE, Biochemistry and molecular biology international, 46(1), 1998, pp. 43-54
The effects of three potential irreversible inhibitors of gamma-aminob
utyrate aminotransferase from Pseudomonas fluorescens were studied in
order to throw more light on the nature of the active site of the enzy
me. The thiol group reagent mercuric chloride inactivated the enzyme i
n a concentration-dependent manner. Inhibition kinetics were consisten
t with a simple bimolecular reaction. The second-order rate constant w
as 4.2 x 10(3) +/- 0.61 M-1 sec(-1). In contrast to either of the subs
trates, the cofactor pyridoxal 5'-phosphate could protect the enzyme f
rom the inhibition, suggesting cysteinyl residues are important for co
factor binding at the active site. p-Chloromercuribenzoic acid produce
d a similar inactivation of the enzyme. 4-Amino-2-fluorobutanoic acid
also inhibited enzymic activity but in this case the inhibition was re
versible and competitive with respect to gamma-aminobutyric acid (GABA
). The inhibitor constant (K-i) was 0.83 +/- 0.44 mM. We found no evid
ence that this fluorinated analogue of GABA could act as a substrate f
or the enzyme.