Specificity of the transport system for neutral amino acids in the hamster intestine

Abstract

The specificity of the active transport system for neutral amino acids has been studied with everted sacs of hamster intestine. Amino acids with modifications or replacements of the carboxyl, amino, or α-hydrogen groups were poorly transported and were poor inhibitors of the transport of other l-amino acids. The carboxyl group must remain free, the amino group must not be in the tertiary or quaternary state, and the α-hydrogen can not be replaced by a methyl group without serious effect on the transport rate. It was concluded that the l-amino acids were distinguished from the d-isomers by the interaction of the carrier with the carboxyl group, the amino group, and the α-hydrogen. The side chain of the amino acid must be nonpolar but there is relatively little restriction on its structure.