AMINO-ACID-TRANSPORT BY HUMAN ERYTHROCYTE-MEMBRANES

The human erythrocyte plasma membrane is permeable to several free ami no acids usually present in the bloodstream. Seven distict routes of e ntry have been described which represent both secondary active transpo rt and facilitated diffusion (passive transport). Additionally, certai n amino acids can enter the cell by simple diffusion, at least to a li mited extent. The function of most of these transport systems is uncle ar, although it has been suggested that the cell can take up certain a mino acids and carry them to various parts of the body. In the case of glutamine, cysteine, and glycine, however, it is believed that the bi osynthesis of the tripeptide glutathione is the primary reason for the ir uptake into the cell. Much of the amino acid transport probably has no function in mature red cells, but might be a remnant of the immatu re cell's needs. This review discusses the various amino acid transpor t systems known to be present in the red cell plasma membrane.