Intestinal transport of certain N-substituted amino acids

¹ Department of Physiology and Biological Chemistry, Harvard Medical School, Boston, Massachusetts
² Departments of Physiology and Biological Chemistry, Harvard Medical School, Boston, Massachusetts

Sarcosine, N,N-dimethylglycine and betaine were transported against concentration gradients by everted sacs of hamster small intestine. These compounds shared a common transport system which differed from that which acted on most neutral l-amino acids. The N-methyl derivatives of glycine, while competing with each other, had no effect on the transport of l-valine. Furthermore, l-valine and l-methionine, which were powerful inhibitors of the transport of most other neutral l-amino acids, had little effect on the absorption of betaine. Two other N-substituted amino acids, l-proline and hydroxy-l-proline, possessed affinity for both transport systems, a greater affinity being shown for the betaine carrier than for the neutral amino acid carrier. It is postulated that the transport system for N-substituted amino acids is important for the absorption of l-proline and hydroxy-l-proline in vivo.