title: Inhibition of 4-aminobutyrate aminotransferase from Pseudomonas fluorescens by ATP.
abstract: The enzyme 4-aminobutyrate aminotransferase (EC 2.6.1.19) isolated from Pseudomonas fluorescens was inhibited by the nucleotide ATP in an apparent competitive manner (Ki = 10.4 mM). This reversible effect was antagonized by the substrate GABA, whose apparent Km was increased from 0.6 mM to 2 mM in the presence of 20 mM ATP, suggesting that ATP interferes with GABA binding to the active site of the enzyme. The apparent Km with respect to the second substrate alpha-ketoglutarate was also increased, although to a lesser extent, whereas the cofactor pyridoxal 5'-phosphate was unable to influence the inhibition by ATP. The ATP structural analogues ADP, CTP and XTP were also able to inhibit the enzyme to a similar extent. These data indicate that GABA concentrations within the bacterial cell can be regulated by the action of ATP on 4-aminobutyrate aminotransferase. In addition, because the inhibition by ATP is similar to the inhibition of the enzyme from mammalian brain, the bacterial enzyme could provide a convenient source of the enzyme for studies of drug effects on brain GABA metabolism in vitro.
authors.affiliation: Laboratory of Neurochemistry, Indiana University School of Medicine, Evansville 47712.
authors.forename: G
authors.initials: G
authors.lastname: Tunnicliff
mesh_terms: D000612:4-Aminobutyrate Transaminase / Q000037:antagonists & inhibitors* / Q000302:isolation & purification; D000244:Adenosine Diphosphate / Q000378:metabolism / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology*; D001667:Binding, Competitive; D003570:Cytidine Triphosphate / Q000494:pharmacology; D007700:Kinetics; D011551:Pseudomonas fluorescens / Q000187:drug effects / Q000201:enzymology*; D012265:Ribonucleotides / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism / Q000494:pharmacology
chemical_list: D012265:Ribonucleotides; D005680:gamma-Aminobutyric Acid; D000244:Adenosine Diphosphate; C065326:xanthosine 5'-triphosphate; D003570:Cytidine Triphosphate; D000255:Adenosine Triphosphate; D000612:4-Aminobutyrate Transaminase