Ho P P, Young A L, Walters P C
Enzyme. 1975;19(4):244-55. doi: 10.1159/000458997.
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.
4-氨基丁酸转氨酶（GABA-T，4-氨基丁酸α-酮戊二酸转氨酶，EC 2.6.1.19）是一种使抑制性神经递质GABA失活的酶，但其药理功能尚不确定。通过DEAE-纤维素色谱法分离出豚鼠脑GABA-T的两种形式，分别命名为GABA-T-I和II，对应于一种阴离子形式和一种阳离子形式。这些酶被高浓度的阳离子形式所抑制。这些酶被高浓度的α-酮戊二酸（α-KG）所抑制。在pH 7.9和1 mmol/L α-KG条件下测定时，GABA的动力学常数为0.74 mmol/L。GABA-T活性受到氯离子和其他阴离子的抑制。动力学分析表明氯离子是GABA的竞争性抑制剂，但GABA-T-I和II的Ki值不同（分别为120和60 mmol/L）。在醋酸根离子和乳酸根离子上也观察到了类似程度的差异。这些结果表明，GABA-T-II可能调节抑制性神经元中的GABA水平，并且可能发挥与单胺氧化酶在其他突触中所表现出的类似功能作用。
