Absorption of glycine and L-alanine by the human jejunum.

Most, if not all, ingested protein is degraded into amino acids, which are then absorbed. Absorption of amino acids has been studied in intact animals, everted gut sacs, and in other preparations of intestine. These studies have been reviewed recently (1, 2). Comparatively little is known, however, about amino acid absorption in the human. Kuroda and Gimbel (3) showed that when racemic amino acids were placed in the isolated ileal loop of a patient operated on for ulcerative colitis, the L-isomer disappeared faster than the D-isomer. Cummins (4) reported a directly proportional increase in the amount of DLmethionine that disappeared from a length of gut when the concentration of the amino acid was doubled. The kinetics of absorption of L-methionine at various sites in the human small intestine were determined by Schedl and Clifton (5). The uptake of certain amino acids by human intestinal biopsy specimens is dependent, at least in part, on active transport (6, 7). This report presents results of studies on absortion of glycine and L-alanine in human subjects. These amino acids were chosen for study because considerable information is available about their absorption by in vitro preparations. Glycine and L-alanine in man appear to be absorbed by active transport processes and to share a common absorptive pathway for which L-alanine has greater affinity. These findings agree with the results of studies in tissue preparations.