Competition for intestinal transport among five neutral amino acids

¹ Gastroenterology Unit, National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, Bethesda, Maryland

Rates of transport against a concentration gradient by everted segments of hamster small intestine were determined for increasing concentrations of glycine and l-alanine, each in the presence of 2 mm l-leucine. By plotting the data according to Lineweaver and Burk the results were compared to those obtained in similar experiments performed in the absence of l-leucine. The results suggest that inhibition of glycine or l-alanine transport by l-leucine is competitive. Values for K_t, the amino acid concentration at which half-maximal transport is observed, were used to calculate predicted inhibitory effects among the several amino acids studied. The inhibitory effects were determined experimentally and were found to be in approximate agreement with the predicted values, suggesting that the mutual transport inhibitions among the monoaminomonocarboxylic acids are competitive, and that all the amino acids studied share the same transport mechanism.

Key Words: competitive inhibition active transport • hamster • small intestine

Submitted on July 23, 1964