Rajendran V M, Berteloot A, Ishikawa Y, Khan A H, Ramaswamy K
Biochim Biophys Acta. 1984 Dec 19;778(3):443-8. doi: 10.1016/0005-2736(84)90392-4.
The characteristics of carnosine (beta-alanyl-L-histidine) transport have been studied using purified brush-border membrane vesicles from mouse small intestine. Uptake curves did not exhibit any overshoot phenomena, and were similar under Na+, K+ or choline+ gradient conditions (extravesicular greater than intravesicular). However, uptake of histidine showed an overshoot phenomenon in the presence of a Na+-gradient. There was no detectable hydrolysis of carnosine during 15 min of incubation with membrane vesicles under conditions used for transport experiments. Analysis of intravesicular contents further showed the complete absence of the constituent free amino acids of carnosine, and indicates that intact carnosine is transported. Studies on the effect of concentration on peptide uptake revealed that transport occurred by a saturable process conforming to Michaelis-Menten kinetics with a Km of 9.6 +/- 1.4 mM and a Vmax of 2.9 +/- 0.2 nmol/mg protein per 0.4 min. Uptake of carnosine was inhibited by both di- and tripeptides with a maximum inhibition of 68% by glycyl-L-leucyltyrosine. These results clearly demonstrate that carnosine is transported intact by a carrier-mediated, Na+-independent process.
利用从小鼠小肠纯化得到的刷状缘膜囊泡，对肌肽（β-丙氨酰-L-组氨酸）的转运特性进行了研究。摄取曲线未表现出任何过冲现象，并且在Na⁺、K⁺或胆碱⁺梯度条件下（囊泡外大于囊泡内）相似。然而，在存在Na⁺梯度的情况下，组氨酸的摄取表现出过冲现象。在用于转运实验的条件下，膜囊泡孵育15分钟期间未检测到肌肽的水解。对囊泡内成分的分析进一步表明完全不存在肌肽的组成性游离氨基酸，并表明完整的肌肽被转运。关于浓度对肽摄取影响的研究表明，转运通过符合米氏动力学的可饱和过程发生，Km为9.6±1.4 mM，Vmax为每0.4分钟2.9±0.2 nmol/mg蛋白质。二肽和三肽均抑制肌肽的摄取，甘氨酰-L-亮氨酰酪氨酸的最大抑制率为68%。这些结果清楚地表明，肌肽通过载体介导的、不依赖Na⁺的过程完整地被转运。
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