Steel R B, Smith C H, Kelley L K
Am J Physiol. 1982 Jul;243(1):C46-51. doi: 10.1152/ajpcell.1982.243.1.C46.
Amino acid uptake by human placental tissue is regulated by intracellular amino acids. alpha-Aminoisobutyric acid (AIB) uptake was reduced at intracellular AIB concentrations of 0.8 mM. The magnitude of reduction increased sharply between 1 and 3 mM and reached a maximum of 45% at 5 mM. Suppression was specific to the "A" system. It occurred only when both the amino acid used for preloading and that used as an uptake substrate were active with that system. In the "L" system, facilitation apparently occurs, and in the "ASC" system there is no apparent effect. The system specificity as well as other evidence indicated that suppression is caused by substrate present intracellularly rather than by dilution of extracellular substrate. Suppression was independent of inhibitors of protein synthesis and was not seen in membrane vesicles prepared from preloaded tissue, indicating that intracellular substrate interacts directly with the carrier (transinhibition) rather than altering its synthesis or degradation. The A system transinhibition has the potential to regulate syncytial uptake in vivo and limit variation due to changes in maternal plasma amino acid concentration.
人胎盘组织对氨基酸的摄取受细胞内氨基酸的调节。当细胞内α-氨基异丁酸（AIB）浓度为0.8 mM时，AIB的摄取减少。在1至3 mM之间，减少幅度急剧增加，在5 mM时达到最大降幅45%。这种抑制作用对“A”系统具有特异性。只有当用于预加载的氨基酸和用作摄取底物的氨基酸都通过该系统起作用时，才会发生抑制。在“L”系统中，显然会出现促进作用，而在“ASC”系统中则没有明显影响。系统特异性以及其他证据表明，抑制是由细胞内存在的底物引起的，而不是由细胞外底物的稀释导致的。抑制作用与蛋白质合成抑制剂无关，并且在从预加载组织制备的膜囊泡中未观察到，这表明细胞内底物直接与载体相互作用（反抑制），而不是改变其合成或降解。A系统反抑制有可能调节体内合体细胞摄取，并限制由于母体血浆氨基酸浓度变化而引起的变化。
