Amino acid distribution in human blood. A significant pool of amino acids is adsorbed onto blood cell membranes.

The recently published existence of a pool of amino acids absorbed onto the blood cell membranes in the rat has provided a new insight into the role of the blood cell amino acid pools, in the context of tissue-blood amino acid transport and their metabolic relationships. In the present study, this pool has been measured in a large (n = 40) representative healthy human population. This pool represents 9% of the blood cell amino acids, which is somewhat lower but in the same order as that previously measured in the rat. The inside-erythrocyte and plasma pools have also been quantified, giving an inside to outside ratio of 1.32 for the combined total amino acids. Statistically significant age related changes in the different blood compartments were detected for some amino acids (aspartate, asparagine, glutamine, tyrosine, methionine, phenylalanine, tryptophan and lysine) as well as for the ratio of tryptophan to the large neutral amino acids. The results obtained emphasize the importance of the amino acid red blood cell pool and assign to it the same order as the plasma pool. The results also feature the membrane-attached pool of some specific amino acids, ie taurine, glutamine, glutamate, aspartate and valine.