Amino group requirement for in vitro intestinal transport of amino acids

¹ Department of Biophysics, University of Buffalo School of Medicine; and Radioisotope Service, Veterans Administration Hospital, Buffalo, New York

The amino group requirement for transintestinal transport of amino acids against a concentration gradient was investigated using hamster everted intestinal sacs. Although glycine (5 x 10^–3 m) was transported against a concentration gradient, acetic acid was not. Similarly, l-phenylalanine was transported, whereas phenylpyruvic acid, phenylpropionic acid, phenyllactic acid, and cinnamic acid were not. l-Tryptophan was transported, but indolyllactic acid was not. The amino group was thus essential for transport by this system. n-Methylglycine and l-proline were accumulated from mucosa to serosa against a concentration gradient. Hence, one hydrogen of the amino group can be replaced. However, n-phenylglycine was not accumulated across these preparations, suggesting that the moiety replacing the amino hydrogen can not be sterically bulky. -l-Alanine was transported against a concentration gradient from mucosa to serosa, but ß-alanine was not. This is in contrast to other systems which accumulate ß-alanine against a concentration gradient. Anthranilic acid, with the amino group in a relative ß position, was also not accumulated across everted intestinal sacs.