Comparison of Procedures for Extracting Free Amino Acids from Polymorphonuclear Leukocytes

We studied five methods for extracting amino acids from human polymorphonuclear leukocytes. Both the use of cell lysis and of a deproteinizing agent interfere with quanti-tative determination of the amino acids, basic amino acids being the most sensitive to the extraction procedure. Among the methods used, disruption of the cells by freezing-thawing is the best method for extracting all the amino acids. Taurine is the only amino acid extracted in the same amount by all the methods studied, and it rep-resents half of the intracellular pool. All mammalian tissues so far studied, including leu-kocytes (1, 2) have a similar amino acid composition (3, 4). Enzyme deficiencies in amino acid metabolism (5) and the accumulation of cystine during cystinosis have been demonstrated in leukocytes (6, 7). The in-tragranulocytic amino acid pool is related to nutritional factors, so that in hypoproteinemia there is a marked decrease in the concentrations of some amino acids (8). Data on free amino acids in leukocytes could thus reflect their variations in other tissues of the organism under various conditions that cause changes. Methods for extracting amino acids vary with the cell type, even from the same organism (9, 10). Moreover, the leukocytes cannot always be consistently lysed (11) and the chemicals used for the amino acid extraction may themselves interfere in the analysis when an ion-exchange procedure is used (12, 13). All these consid-erations led us to compare the different methods for extracting amino acids from leukocytes and to deter-mine their concentrations in these cells as measured after extraction