title: Two forms of 4-aminobutyrate transaminase in guinea pig brain.
abstract: 4-Aminobutyrate transaminase (GABA-T, 4-aminobutyrate alpha-oxoglutrate aminotransferase, EC 2.6.1.19) is an enzyme that inactivates the inhibitory neurotransmitter, GABA, but its pharmacological function is uncertain. Two forms of guiena pig brain GABA-T were isolated by DEAE-cellulose chromatography and designated as GABA-T-I and II, corresponding to an anionic and a cationic form. The enzymes were inhibited by high concentrations of a cationic form. The enzymes were inhibited by high concentrations of alpha-oxoglutrate (alpha-KG). Kinetic consists for GABA, when determined at pH 7.9 adn 1 mmol/l alpha-KG, were 0.74 mmol/l. GABA-T activity was inhibited by chloride and other anions. Kinetic analysis revealed chloride ion as a conpetitive inhibitor against GABA, but the Ki values differed among GABA-T-I and II (Ki equals 120 and 60 mmol/l, respectively). Similar  degrees of difference were observed with acetate and lactate ion. These results suggest that GABA-T-II may regulate the GABA level in the inhibitory neurons and may play a similar functional role as that exhibited by monoamine oxidase in other synapses.
mesh_terms: D000612:4-Aminobutyrate Transaminase / Q000302:isolation & purification / Q000378:metabolism*; D000085:Acetates / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000201:enzymology*; D001965:Bromides / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D002848:Chromatography, DEAE-Cellulose; D004789:Enzyme Activation / Q000187:drug effects; D005459:Fluorides / Q000494:pharmacology; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D007773:Lactates / Q000494:pharmacology; D009243:NAD / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D013997:Time Factors; D000637:Transaminases / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: D000085:Acetates; D001965:Bromides; D002712:Chlorides; D007527:Isoenzymes; D007773:Lactates; D009243:NAD; D005680:gamma-Aminobutyric Acid; D012964:Sodium; D000637:Transaminases; D000612:4-Aminobutyrate Transaminase; D005459:Fluorides