Stieger B, O'Neill B, Krähenbühl S
Department of Internal Medicine, University Hospital, Zürich, Switzerland.
Biochem J. 1995 Jul 15;309 ( Pt 2)(Pt 2):643-7. doi: 10.1042/bj3090643.
In the presence of a 100 mM Na+ gradient, transport of L-carnitine into rat renal brush-border-membrane vesicles was linear over 30 s and showed an overshoot at 5 min. The uptake of L-carnitine was clearly less active in the presence of other cations such as Li+, K+, Cs+ or choline. In the presence of a Na+ gradient, L-carnitine uptake after 20 s was much higher for chloride as an anion than for SCN-, NO3-, gluconate or SO4(2-). In comparison with conditions with inside positive or no membrane potential, transport was higher in vesicles with an inside negative membrane potential, suggesting an electrogenic mechanism. The kinetic characterization of the Na(+)-dependent portion of L-carnitine transport revealed two transport systems with Km values of 17.4 +/- 3.9 microM and 15.0 +/- 6.0 mM, respectively. The transport could be inhibited in a concentration-dependent fashion by structural analogues such as butyrobetaine, L-acetylcarnitine, trimethyl-lysine and D-carnitine, but not by L-arginine or glycinebetaine.
在存在100 mM Na⁺梯度的情况下，L-肉碱转运至大鼠肾刷状缘膜囊泡中的过程在30秒内呈线性，并在5分钟时出现超调现象。在存在其他阳离子如Li⁺、K⁺、Cs⁺或胆碱的情况下，L-肉碱的摄取明显不那么活跃。在存在Na⁺梯度的情况下，作为阴离子的氯离子存在时，20秒后L-肉碱的摄取比SCN⁻、NO₃⁻、葡萄糖酸盐或SO₄²⁻时要高得多。与膜内为正电位或无膜电位的情况相比，膜内为负电位的囊泡中转运更高，提示存在电生成机制。L-肉碱转运的Na⁺依赖性部分的动力学特征显示有两个转运系统，其Km值分别为17.4±3.9 μM和15.0±6.0 mM。该转运可被结构类似物如丁酸甜菜碱、L-乙酰肉碱、三甲基赖氨酸和D-肉碱以浓度依赖性方式抑制，但不受L-精氨酸或甘氨酸甜菜碱抑制。
