Iioka H, Moriyama I, Hino K, Ichijo M
Nihon Sanka Fujinka Gakkai Zasshi. 1986 Mar;38(3):355-60.
Using microvillous (brush border) membrane vesicles prepared from human term placenta, the uptake of L-glutamine was studied using a rapid filtration technique. The uptake of L-glutamine into the vesicles was osmotically sensitive. A Na+ electrochemical gradient (extravesicular greater than intravesicular) stimulated the initial rate of L-glutamine uptake and the Na+ dependent uptake of L-glutamine into vesicles showed a typical overshoot phenomenon. This overshoot and the initial rate of uptake were markedly increased when the intravesicular space was rendered electrically more negative by membrane diffusion potentials, induced by the use of highly permeant anions. A similar stimulation of L-glutamine uptake was observed when membrane potential (inside negative) was imposed by K+ diffusion potentials via valinomycin. These results indicated that a sodium dependent uptake of L-glutamine into the microvillous membrane vesicles was dependent on the electrical potential difference of membrane. The initial rate of L-glutamine transport exhibited saturation kinetics with respect to L-glutamine concentration; the apparent Km of 0.42 mM and Vmax of 1.54 nmol/mg protein/20 sec were calculated. The uptake of L-glutamine into the vesicles was competitively inhibited by L-alanine.
利用从足月人胎盘中制备的微绒毛（刷状缘）膜囊泡，采用快速过滤技术研究了L-谷氨酰胺的摄取情况。L-谷氨酰胺进入囊泡的摄取对渗透压敏感。Na⁺电化学梯度（囊泡外大于囊泡内）刺激了L-谷氨酰胺摄取的初始速率，并且L-谷氨酰胺依赖于Na⁺进入囊泡的摄取表现出典型的过冲现象。当通过使用高渗透性阴离子诱导的膜扩散电位使囊泡内空间在电学上更负时，这种过冲和摄取的初始速率显著增加。当通过缬氨霉素由K⁺扩散电位施加膜电位（内侧为负）时，观察到对L-谷氨酰胺摄取的类似刺激。这些结果表明，L-谷氨酰胺依赖于钠进入微绒毛膜囊泡的摄取取决于膜的电势差。L-谷氨酰胺转运的初始速率相对于L-谷氨酰胺浓度表现出饱和动力学；计算得出表观Km为0.42 mM，Vmax为1.54 nmol/mg蛋白质/20秒。L-丙氨酸竞争性抑制L-谷氨酰胺进入囊泡的摄取。
