Kinetics of intestinal active transport of five neutral amino acids

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 Kt, 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 Kt for α-aminoisobutyric acid was much higher than the others. Values for Vmax, 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.