Kanner B I, Bendahan A
Department of Biochemistry, Hadassah Medical School, Hebrew University, Jerusalem, Israel.
Proc Natl Acad Sci U S A. 1990 Apr;87(7):2550-4. doi: 10.1073/pnas.87.7.2550.
Electrogenic sodium- and chloride-dependent gamma-aminobutyric acid (GABA) transport in crude synaptosomal membrane vesicles is partly inhibited by saturating levels of either of the substrate analogues cis-3-aminocyclohexanecarboxylic acid (ACHC) or beta-alanine. However, both of them together potently and fully inhibit the process. Transport of beta-alanine, which exhibits an apparent Km of about 44 microM, is also electrogenic and sodium and chloride dependent and competitively inhibited by GABA with a Ki of about 3 microM. This value is very similar to the Km of 2-4 microM found for GABA transport. On the other hand, ACHC does not inhibit beta-alanine transport at all. Upon solubilization of the membrane proteins with cholate and fractionation with ammonium sulfate, a fraction is obtained which upon reconstitution into proteoliposomes exhibits 4- to 10-fold-increased GABA transport. This activity is fully inhibited by low concentrations of ACHC and is not sensitive at all to beta-alanine. GABA transport in this preparation exhibits an apparent Km of about 2.5 microM and it is competitively inhibited by ACHC (Ki approximately 7 microM). These data indicate the presence of two GABA transporter subtypes in the membrane vesicles: the A type, sensitive to ACHC, and the B type, sensitive to beta-alanine.
在粗制突触体膜囊泡中，依赖钠和氯的γ-氨基丁酸（GABA）的电致转运可被底物类似物顺式-3-氨基环己烷羧酸（ACHC）或β-丙氨酸中的任一种饱和水平部分抑制。然而，两者共同作用时可有效且完全抑制该过程。β-丙氨酸的转运表现出约44微摩尔的表观Km值，也是电致的且依赖钠和氯，并被GABA竞争性抑制，其抑制常数（Ki）约为3微摩尔。该值与GABA转运的2 - 4微摩尔的Km值非常相似。另一方面，ACHC根本不抑制β-丙氨酸的转运。用胆酸盐溶解膜蛋白并用硫酸铵分级分离后，可得到一个组分，将其重新组装到蛋白脂质体中时，GABA转运增加4至10倍。该活性可被低浓度的ACHC完全抑制，且对β-丙氨酸完全不敏感。该制剂中的GABA转运表现出约2.5微摩尔的表观Km值，并被ACHC竞争性抑制（Ki约为7微摩尔）。这些数据表明膜囊泡中存在两种GABA转运体亚型：对ACHC敏感的A型和对β-丙氨酸敏感的B型。
