Matthews R H, Zand R
Biochim Biophys Acta. 1979 Jun 13;554(1):227-33. doi: 10.1016/0005-2736(79)90020-8.
Methionine had been observed to interact with two principal transport systems for amino acids in mammalian cells, the A and L systems. The present study of methionine transport and of exchange processes through system A arose in the course of a study to define the specificity of a transinhibition effect caused by cysteine. Methionine uptake through two transport systems in the S37 cell was confirmed by the occurrence of a biphasic double-reciprocal plot for labeled methionine uptake. Preloading cells with methionine stimulated labeled histidine uptake through systems A and L. Efflux of labeled methionine from cells was stimulated by histidine in a biphasic manner, so that bothe systems A and L can be used for exchange when methionine is the intracellular amino acid. Aminocycloheptanecarboxylic acid elicited exchange efflux of labeled methionine only through system L. ALPHA-Aminoisobutyric acid and N-methyl-alpha-aminoisobutyric acid both stimulated efflux of labeled N-methyl-alpha-aminoisobutyric acid from S37 cells. These findings are interpreted a showing that transport system A is capable of functioning as an exchange system depending upon the identity of intracellular and extracellular substrates available.
已观察到蛋氨酸与哺乳动物细胞中两种主要的氨基酸转运系统，即A系统和L系统相互作用。目前对蛋氨酸转运及通过A系统的交换过程的研究，是在一项旨在确定半胱氨酸引起的转抑制效应特异性的研究过程中展开的。通过对标记蛋氨酸摄取的双相双倒数图的出现，证实了S37细胞中蛋氨酸通过两种转运系统的摄取。用蛋氨酸预加载细胞刺激了通过A系统和L系统的标记组氨酸摄取。组氨酸以双相方式刺激标记蛋氨酸从细胞中流出，因此当蛋氨酸是细胞内氨基酸时，A系统和L系统均可用于交换。氨基环庚烷羧酸仅通过L系统引起标记蛋氨酸的交换流出。α-氨基异丁酸和N-甲基-α-氨基异丁酸均刺激标记的N-甲基-α-氨基异丁酸从S37细胞中流出。这些发现被解释为表明转运系统A能够根据细胞内和细胞外可用底物的特性作为交换系统发挥作用。
