Oxender D L, Lee M, Cecchini G
J Biol Chem. 1977 Apr 25;252(8):2680-3.
Balb/3T3 mouse cells grown in cell culture contain the A and L systems for neutral amino acid transport. L-Alanine was used as a test amino acid for the A system and L-leucine for the L system. Transport activities for both transport systems are altered as the growth conditions for the cells are altered. When cell growth was arrested by allowing cells to approach confluency, or by the removal of serum or by the addition of protein synthesis inhibitors, System A transport activity decreased and System L activity increased significantly. The content of the cellular amino acids increased 2- to 3-fold whenever cell growth was arrested by the conditions stated above. Increased cellular amino acids, therefore, are associated with decreased transport activity of System A and increased activity of System L. Altering cellular amino acids by loading or depleting the cells produced the predicted responses for the rapidly exchanging L-system but System A was less responsive. It is possible that regulatory mechanisms operate for the A system other than the direct action of alterations in cellular amino acid levels. The implications of the amino acid transport activity changes observed here on various studies on the role of transport in cell growth regulation and malignant transformation are discussed.
在细胞培养中生长的Balb/3T3小鼠细胞含有用于中性氨基酸转运的A和L系统。L-丙氨酸用作A系统的测试氨基酸，L-亮氨酸用作L系统的测试氨基酸。随着细胞生长条件的改变，两个转运系统的转运活性都会发生变化。当通过使细胞接近汇合、去除血清或添加蛋白质合成抑制剂来阻止细胞生长时，A系统的转运活性降低，L系统的活性显著增加。每当通过上述条件阻止细胞生长时，细胞内氨基酸含量会增加2至3倍。因此，细胞内氨基酸增加与A系统转运活性降低和L系统活性增加相关。通过加载或耗尽细胞来改变细胞内氨基酸，会对快速交换的L系统产生预期的反应，但A系统的反应较小。除了细胞内氨基酸水平改变的直接作用外，可能还有其他调节机制作用于A系统。本文讨论了此处观察到的氨基酸转运活性变化对各种关于转运在细胞生长调节和恶性转化中作用的研究的影响。
