Low-affinity intestinal L-aspartate transport with 2:1 coupling stoichiometry for Na+/Asp.
Low-affinity intestinal L-aspartate transport with 2:1 coupling stoichiometry for Na+/Asp.
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Na /Asp 的低亲和力肠道 L-天冬氨酸转运采用 2:1 耦合化学计量。
DOI：
10.1152/ajpcell.1988.255.6.c737
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发表时间：
1988
期刊：
影响因子：
--
通讯作者：
Kimmich,GA
中科院分区：
文献类型：
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作者：
Wingrove,TG;Kimmich,GA
从鸡小肠中分离出的上皮细胞用于定义低亲和力 (Km = 4.1 mM) L-天冬氨酸转运系统的离子和电特性。 L-谷氨酸和 D-天冬氨酸，但不是 D-谷氨酸，被发现可以抑制 L-天冬氨酸流入，表明该摄取系统具有类似于先前描述的相同细胞中的高亲和力 (Km = 16 microM) 酸性氨基酸转运蛋白的底物特异性。低亲和力吸收依赖于 Na+，希尔系数 (n) 为 1.4。细胞内 K+ 适度增强天冬氨酸流入，但不是必需的，并且这种反应受细胞内 pH 值变化的调节。天冬氨酸的 Na+ 依赖性吸收是电中性的，这通过在 K+ 梯度存在下对阴离子梯度或缬氨霉素引起的 delta psi 的显着变化不敏感来证明。由于上述特性可以与多种传输模型相一致，因此进行了δNa+-δAsp耦合化学计量的直接测量。耦合比被确定为大约2.0。建议建立肠道 Na+ 依赖性 L-Asp 转运模型，其中每个转运周期涉及 2Na+:1Asp+ 的向内转运和 K+ 或 H+ 在一系列净电中性事件中的向外转运。
Epithelial cells isolated from chick small intestine were used to define the ionic and electrical characteristics of a low-affinity (Km = 4.1 mM) L-aspartate transport system. L-Glutamate and D-aspartate, but not D-glutamate, were found to inhibit L-aspartate influx, suggesting that this uptake system has a substrate specificity similar to that previously described for a high-affinity (Km = 16 microM) acidic amino acid transporter in the same cells. Low-affinity uptake is Na+ dependent with a Hill coefficient (n) of 1.4. Intracellular K+ moderately enhances but is not required for aspartate influx, and this response is modulated by changes in intracellular pH. The Na+-dependent uptake of aspartate is electroneutral, as evidenced by insensitivity to pronounced changes in delta psi induced by anion gradients or valinomycin in the presence of K+ gradients. Because the above characteristics can be consistent with several transport models, direct measurement of delta Na+-delta Asp coupling stoichiometry were performed. The coupling ratio was determined to be approximately 2.0. A model for intestinal Na+-dependent L-Asp transport is suggested in which each transport cycle involves inward transfer of 2Na+:1Asp+ and outward transfer of K+ or H+ in a net electroneutral set of events.