Gazzola G C, Dall'Asta V, Guidotti G G
J Biol Chem. 1980 Feb 10;255(3):929-36.
The transport of neutral amino acids and their interactions for uptake have been studied in skin-derived-diploid human fibroblasts cultured at confluency. Properly timed preincubations in a medium defined in composition and requirements have been adopted to control size of internal amino acid pools and regulatory interferences affecting amino acid transport. L-Proline, L-alanine, and L-leucine were used as natural amino acid substrates. Amino acid uptake and exchange with preaccumulated molecules have been measured under conditions approaching initial entry rates in the absence and in the presence of Na+ and of transport-specific model substrates. Cultured human fibroblasts were found to contain three neutral amino acid transport systems: A, ASC, and L. L-Proline was taken up preferentially by System A. System ASC appeared to mediate the largest fraction of L-Leucine entered the cells mainly by the Na+-independent System L. Preaccumulation of the cells with Site A-reactive amino acids caused trans-inhibition of the activity of System A. The activity of System L was strongly trans-stimulated in cells preloaded with Site L-reactive amino acids. The inward transport of L-alanine was trans-inhibited by internal Site A-reactive amino acids and trans-stimulated by preaccumulated L-alanine exchanging with the external amino acid through the operation of System ASC.
在汇合培养的皮肤来源的二倍体人成纤维细胞中，对中性氨基酸的转运及其摄取相互作用进行了研究。采用在成分和需求明确的培养基中进行适当时间预孵育的方法，以控制细胞内氨基酸池的大小以及影响氨基酸转运的调节干扰。L-脯氨酸、L-丙氨酸和L-亮氨酸用作天然氨基酸底物。在不存在和存在Na+以及转运特异性模型底物的情况下，在接近初始进入速率的条件下测量氨基酸摄取和与预积累分子的交换。发现培养的人成纤维细胞含有三种中性氨基酸转运系统：A、ASC和L。L-脯氨酸优先被系统A摄取。系统ASC似乎介导了大部分L-亮氨酸主要通过不依赖Na+的系统L进入细胞。用A位点反应性氨基酸预积累细胞会导致系统A活性的反式抑制。在预加载L位点反应性氨基酸的细胞中，系统L的活性受到强烈的反式刺激。L-丙氨酸的内向转运受到细胞内A位点反应性氨基酸的反式抑制，并通过系统ASC的运作与外部氨基酸交换预积累的L-丙氨酸而受到反式刺激。
