Kinetics of intestinal active transport of 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 five monoaminomonocarboxylic acids. Values varied considerably from animal to animal. A graph of reciprocal of transport rate as a function of reciprocal of initial amino acid concentration revealed a linear relationship for each amino acid. Values for K_t, the concentration at which half-maximal transport is observed, diminished with increasing length of side chain for glycine, l-alanine, l-valine, and l-leucine. The K_t for -aminoisobutyric acid was much higher than the others. Values for V_max, the apparent limiting transport rate, decreased as chain length increased. With increasing initial amino acid concentration transport rate rose to a maximum and then declined. At concentrations producing this decline no gross mucosal damage was noted. The apparent inhibitory effect of these high concentrations was not a permanent one.

Key Words: intestinal absorption • small intestine • hamster water transport • glycine • l-alanine • l-leucine • l-valine • -aminoisobutyric acid

Submitted on July 23, 1964

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