Benderoff S, Blostein R, Johnstone R M
Membr Biochem. 1978;1(1-2):89-106. doi: 10.3109/09687687809064161.
We studied amino acid transport in sheep red blood cells (RBCs) as a function of cell maturation. Transport of amino acids is decreased strikingly in the mature mammalian RBC compared to the immature reticulocyte. Blood obtained 5-6 days after massive bleeding was fractionated on dextran gradients. In the mature erythrocyte amino acids are taken up only slowly, and in the normal experimental interval (60 min) the concentration in the cell does not reach that of the medium. In contrast, the reticulocyte-rich (top) fraction (50-90% reticulocyte) accumulates certain amino acids, particularly histidine, methionine, and leucine. The underlying process is ATP-independent and Na+-insensitive, and has properties consistent with exchange diffusion, i.e., accelerated uptake or efflux when unlabeled solute is present on the trans side. The process is apparent not only in intact cells but also in resealed ghosts. The decrease in activity of amino acid transport is a function of red cell maturation. Thus it can be shown that (a) separation of cells according to their density 1, 2, and 3 weeks after bleeding leads to progressively lower amino acid transport activity with increasing cell density; and (b) during in vitro long-term incubation at 37 degrees C of reticulocyte-rich, unfractionated blood (5-10% reticulocytes), amino acid transport decreases while red cell integrity is maintained, as evidenced by the retention of a normal K+ gradient and the absence of hemolysis. The progressive loss is seen with resealed ghosts as well as with intact cells. Not all the amino acids examined participate in this exchange process. The most actively exchanged are histidine, leucine, methionine, and phenylalanine. Glycine, proline, arginine, and a-amino isobutyric acid do not participate in the exchange process.
我们研究了绵羊红细胞（RBCs）中氨基酸转运作为细胞成熟度的函数。与未成熟的网织红细胞相比，成熟哺乳动物红细胞中的氨基酸转运显著降低。大量出血后5 - 6天采集的血液在葡聚糖梯度上进行分级分离。在成熟红细胞中，氨基酸摄取缓慢，在正常实验间隔（60分钟）内，细胞内浓度未达到培养基中的浓度。相比之下，富含网织红细胞的（顶部）级分（50 - 90%网织红细胞）积累某些氨基酸，特别是组氨酸、蛋氨酸和亮氨酸。潜在过程不依赖ATP且对Na +不敏感，具有与交换扩散一致的特性，即当未标记溶质存在于转运侧时，摄取或流出加速。该过程不仅在完整细胞中明显，在重新封闭的血影中也明显。氨基酸转运活性的降低是红细胞成熟度的函数。因此可以表明：（a）出血后1、2和3周根据细胞密度分离细胞，随着细胞密度增加，氨基酸转运活性逐渐降低；（b）在37℃下对富含网织红细胞的未分级血液（5 - 10%网织红细胞）进行体外长期孵育时，氨基酸转运降低，同时红细胞完整性得以维持，正常K +梯度的保留和溶血的不存在证明了这一点。重新封闭的血影以及完整细胞都出现了这种逐渐丧失的情况。并非所有检测的氨基酸都参与此交换过程。最活跃交换的是组氨酸、亮氨酸、蛋氨酸和苯丙氨酸。甘氨酸、脯氨酸、精氨酸和α - 氨基异丁酸不参与交换过程。
