Transfer of alanine isomers by rat small intestine.

1. A study was made of the transfer of L-alanine, D-alanine and beta-alanine by sacs of everted small intestine of the rat.2. D-Alanine and beta-alanine are transported against a concentration gradient and in this respect resemble L-alanine.3. Transfer of all three isomers was stimulated in presence of glucose, but stimulation was much greater with D-alanine and beta-alanine.4. Transfer of all three isomers was inhibited by galactose.5. The effect of hexoses on amino acid transfer was relatively independent of the effect on fluid transfer.6. L-Methionine inhibited transfer of the three isomers in descending order, L-alanine, D-alanine and beta-alanine, while the magnitude of sarcosine inhibition was in the reverse order.7. At the concentration used (1 mM), L-alanine was transferred mostly by the methionine carrier, and beta-alanine mostly by the sarcosine carrier. D-Alanine occupied an intermediate position.