Miyamoto Y, Kulanthaivel P, Leibach F H, Ganapathy V
Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta 30912-2100.
Invest Ophthalmol Vis Sci. 1991 Aug;32(9):2542-51.
Characteristics of taurine uptake were investigated in apical membrane vesicles isolated from bovine retinal pigment epithelium. Uptake of taurine into these vesicles was stimulated markedly by the presence of an inwardly directed NaCl gradient across the membrane. The time course of the NaCl gradient-dependent uptake showed an overshoot, indicating a transient accumulation of taurine in the vesicles against a concentration gradient. Monovalent cations other than Na+ did not support taurine uptake. There was also an anion requirement for the uptake system, and Cl- was the most potent among several monovalent anions tested. The NaCl-dependent taurine uptake was stimulated by inside-negative, K+, and H+ diffusion potentials, demonstrating the electrogenic nature of the system. Stoichiometric analysis revealed that two Na+ and one Cl- ions were involved in the translocation of one taurine molecule. The system had an apparent dissociation constant (Kt) of 96 +/- 17 microM and a maximal velocity of 267 +/- 24 pmol/mg of protein over 15 sec. Uptake of radiolabeled taurine was inhibited by excess amounts of unlabeled taurine, hypotaurine, beta-alanine, and gamma-aminobutyric acid. The relative potencies of the amino acids to inhibit taurine uptake were compared in three tissues, the bovine retinal pigment epithelium, the rat kidney, and the human placenta. In the apical membrane vesicles of the pigment epithelium, gamma-aminobutyric acid was many times more potent than taurine itself in inhibiting radiolabeled taurine uptake. However, in the brush border membrane vesicles of the kidney and the placenta, taurine was many times more potent than gamma-aminobutyric acid.(ABSTRACT TRUNCATED AT 250 WORDS)
对从牛视网膜色素上皮分离的顶端膜囊泡中牛磺酸摄取的特性进行了研究。跨膜内向的NaCl梯度显著刺激了牛磺酸进入这些囊泡的摄取。NaCl梯度依赖性摄取的时间进程显示有过冲现象，表明牛磺酸在囊泡中逆浓度梯度短暂积累。除Na⁺外的单价阳离子不支持牛磺酸摄取。摄取系统也需要阴离子，在测试的几种单价阴离子中Cl⁻作用最强。NaCl依赖性牛磺酸摄取受到膜内负电位、K⁺和H⁺扩散电位的刺激，证明了该系统的生电性。化学计量分析表明，一个牛磺酸分子的转运涉及两个Na⁺离子和一个Cl⁻离子。该系统的表观解离常数（Kt）为96±17μM，在15秒内的最大速度为267±24 pmol/mg蛋白质。过量的未标记牛磺酸、亚牛磺酸、β-丙氨酸和γ-氨基丁酸抑制了放射性标记牛磺酸的摄取。比较了三种组织（牛视网膜色素上皮、大鼠肾脏和人胎盘）中氨基酸抑制牛磺酸摄取的相对效力。在色素上皮的顶端膜囊泡中，γ-氨基丁酸在抑制放射性标记牛磺酸摄取方面比牛磺酸本身强许多倍。然而，在肾脏和胎盘的刷状缘膜囊泡中，牛磺酸比γ-氨基丁酸强许多倍。（摘要截短于250字）
