Intestinal transport of cyclic and noncyclic imino acids

• 1.

  1. Employing hamster everted intestinal sacs, the transport of l-phenylalanine and l-proline against a concentration gradient had the following indentical characteristics: spatial distribution of transport, inhibition by absence of Na+ from the medium, inhibition by NaCN but not by propionitrile, lack of effect of added ascorbic acid, and the same temperature coefficient (2.3 for a 10° change), In addition, there was mutual inhibition of transport as measured by the equillibrium quantity. These parameters, hence, were unable to provide a distinction between the mechanism of transport of the amino acid and the amino acid (although genetic data suggest that two distinct, but overlapping, transport systems are involved).

• 2.

  2. A series of noncyclic imino acids of the form

  was also studied for transport against a concentration gradient by the hamster everted small intestine. When X = H, transport occurred with Y = CH₃, but not when Y = CH₂CH₃ or larger groupings. Hence, N-methylglycine likely represents the most “sterically bulky” of these compounds to be transported.

• 3.

  3. Cyclic imino acids of the form

  were transported against a concentration gradient when n = 2 (azetidine-2-carboxylic acid), n = 3 (proline) and n = 4 (pipecolic acid). For n = 1 (aziridine-2-carboxylic acid, lithium salt), the compound did not appear to be transported. Data are presented that cyclic and noncyclic imino acids show cross-inhibition of transport.