Weiss S D, McNamara P D, Pepe L M, Segal S
J Membr Biol. 1978 Sep 29;43(1):91-105. doi: 10.1007/BF01869043.
Glutamine uptake by rat renal brushborder vesicles occurred via two distinct saturable processes with Km values of 0.145 and 8.5 mM which were stimulated by both ionic and sodium gradients with a pH optimum of 6.8--7.1. Glutamic acid uptake also occurred by a two-component system with Km values of 0.016 and 3.60 mM. Both components were stimulated specifically by a sodium gradient. The low Km system for glutamic acid had a pH optimum of 7.2--7.4. Glutamine entry at 0.06 mM was inhibited by a variety of amino acids at 3 mM, including dibasic amino acids, glycine, valine, and phenylalanine. Glutamic acid entry at 0.06 mM was inhibited 20--30% by 3 mM phenylalanine, valine, alpha-aminoisobutyric acid, and glutamine. No metabolic alteration of glutamic acid was observed on incubation with membrane vesicles, but glutamine was significantly hydrolyzed to glutamic acid upon prolonged incubation. Hydrolysis of glutamine was negligible at 15 sec incubation which was employed for measurement of initial rate of entry. These studies provide support for the existence of an uptake system in the brushborder of the renal proximal tubule cell capable of handling the reabsorption of glutamine normally present in glomerular filtrate.
大鼠肾刷状缘小泡对谷氨酰胺的摄取通过两个不同的可饱和过程进行，其Km值分别为0.145和8.5 mM，这两个过程均受到离子梯度和钠梯度的刺激，最适pH为6.8 - 7.1。谷氨酸的摄取也通过一个双组分系统进行，其Km值分别为0.016和3.60 mM。两个组分均受到钠梯度的特异性刺激。谷氨酸的低Km系统最适pH为7.2 - 7.4。0.06 mM的谷氨酰胺进入受到3 mM的多种氨基酸抑制，包括二元氨基酸、甘氨酸、缬氨酸和苯丙氨酸。0.06 mM的谷氨酸进入受到3 mM苯丙氨酸、缬氨酸、α-氨基异丁酸和谷氨酰胺抑制20 - 30%。与膜小泡孵育时未观察到谷氨酸的代谢改变，但长时间孵育后谷氨酰胺可显著水解为谷氨酸。在用于测量初始进入速率的15秒孵育时，谷氨酰胺的水解可忽略不计。这些研究为肾近端小管细胞刷状缘存在一个摄取系统提供了支持，该系统能够处理肾小球滤液中正常存在的谷氨酰胺的重吸收。
