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 α-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.
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Matthews et al. (1965) studied this question.