Smith T C, Robinson S C
J Cell Physiol. 1981 Dec;109(3):507-16. doi: 10.1002/jcp.1041090317.
The effects of H+ on the kinetics of alpha-aminoisobutyric acid (AIB) influx in Ehrlich ascites tumor cells have been investigated at different external Na+ concentrations. Elevation of [H+] in the presence of both high (154 mEq/l) and low (10 mEq/l) external Na+ leads to decreases in the maximum influx (Jmax) and increases in the apparent Michaelis-Menten constant (Km) for influx of AIB. In the virtual absence of external Na+ (0.96 +/- 0.04 mEq/l), alterations in [H+] are without measurable effect on AIB flux. Furthermore, addition of AIB (10 mM) to cell suspensions (pH 5.90) stimulates H+ uptake by the cells in either the presence or absence of Na+. The data are consistent with two kinetic models for Na+-dependent amino acid transport: an order bireactant (Na+-binding necessary before AIB binding) system or a random bireactant system. Both models require that H+ serve as an alternative substrate for Na+. The consistency of the models was tested by fit to data from the present study (not used to evaluate the kinetic parameters) and by prediction of the pH dependence of Na+-dependent amino acid transport compared to earlier studies.
已在不同的细胞外钠离子浓度下研究了氢离子对艾氏腹水瘤细胞中α-氨基异丁酸（AIB）内流动力学的影响。在高（154毫当量/升）和低（10毫当量/升）细胞外钠离子存在的情况下，氢离子浓度升高会导致AIB内流的最大速率（Jmax）降低，且AIB内流的表观米氏常数（Km）增加。在几乎不存在细胞外钠离子（0.96±0.04毫当量/升）的情况下，氢离子浓度的改变对AIB通量没有可测量的影响。此外，在存在或不存在钠离子的情况下，向细胞悬液（pH 5.90）中添加AIB（10毫摩尔）都会刺激细胞摄取氢离子。这些数据与钠离子依赖性氨基酸转运的两种动力学模型一致：有序双反应物（AIB结合前必须结合钠离子）系统或随机双反应物系统。两种模型都要求氢离子作为钠离子的替代底物。通过拟合本研究的数据（未用于评估动力学参数）以及与早期研究相比预测钠离子依赖性氨基酸转运的pH依赖性，对模型的一致性进行了测试。
