Tyrosine residues are essential for the activity of the human placental taurine transporter.
Tyrosine residues are essential for the activity of the human placental taurine transporter.
复制标题
酪氨酸残基对于人胎盘牛磺酸转运蛋白的活性至关重要。
DOI：
10.1016/0005-2736(89)90358-1
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发表时间：
1989
期刊：
影响因子：
--
通讯作者：
Ganapathy,V
中科院分区：
文献类型：
--
作者：
Kulanthaivel,P;Leibach,FH;Mahesh,VB;Ganapathy,V
用四种酪氨酸基团特异性试剂、N-乙酰咪唑、7-氯-4-硝基苯并-2-氧杂-1,3-二唑 (NBD-Cl)、四硝基甲烷和对硝基苯磺酰氟处理人胎盘刷状缘膜囊泡，抑制这些囊泡中 NaCl 梯度驱动的牛磺酸摄取，而不影响囊泡完整性。这些试剂抑制转运蛋白的相对效力按以下顺序排列：四硝基甲烷>NBD-Cl>对硝基苯磺酰氟>N-乙酰基咪唑。 N-乙酰基咪唑的抑制作用可与羟胺可逆，NBD-Cl的抑制作用可与2-巯基乙醇可逆。对对照和 N-乙酰咪唑处理的膜囊泡中牛磺酸摄取的动力学分析表明，抑制主要是由于最大速度的降低。在对照和处理的囊泡中，转运蛋白对牛磺酸的亲和力没有变化。可以保护转运蛋白免受N-乙酰基咪唑诱导的Na+抑制。牛磺酸摄取率对囊外Na+浓度的依赖性呈S形，数据分析表明，每个牛磺酸分子的转运涉及两个Na+离子。结论是，酪氨酸残基对于人胎盘牛磺酸转运蛋白的最佳转运功能至关重要，并且这些关键的酪氨酸残基位于转运蛋白的Na + 结合位点处或附近。
Treatment of human placental brush-border membrane vesicles with four tyrosine group-specific reagents,N-acetylimidazole, 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl), tetranitromethane andp-nitrobenzenesulfonyl fluoride, inhibited NaCl gradient-driven taurine uptake in these vesicles without affecting the vesicle integrity. The relative potency of these reagents to inhibit the transporter was in the following order: tetranitromethane > NBD-Cl >p-nitrobenzenesulfonyl fluoride >N-acetylimidazole. The inhibition byN-acetylimidazole was reversible with hydroxylamine and the inhibition by NBD-Cl was reversible with 2-mercaptoethanol. Kinetic analysis of taurine uptake in control and inN-acetylimidazole-treated membrane vesicles revealed that the inhibition was primarily due to a reduction in the maximal velocity. There was no change in the affinity of the transporter for taurine in control and treated vesicles. The transporter could be protected from theN-acetylimidazole-induced inhibition by Na+. The dependence of taurine uptake rate on extravesicular Na+concentration was sigmoidal and analysis of the data revealed that two Na+ions were involved per transport of one taurine molecule. It is concluded that tyrosine residues are essential for optimal transport function of the human placental taurine transporter and that these critical tyrosine residues are located at or near the Na+-binding site of the transporter.