Transport of glycyl-L-proline by mouse intestinal brush-border membrane vesicles

The characteristics of [14C]glycyl-L-proline transport have been studied using brush-border membrane vesicles from mouse small intestine in order to investigate the transport of nonhydrolyzable peptide across the brush-border membrane. Uptake curves for the peptide did not exhibit overshoot phenomena and were similar under Na+ or K+ gradient conditions (extravesicular greater than intravesicular). However, L-proline was transported by Na+ gradient-dependent system. Analysis of the incubation medium and the intravesicular contents showed that there was negligible hydrolysis of the peptide. Transport of glycyl-L-proline was saturable, conforming to Michaelis-Menten kinetics with a Km of 30.8 +/- 1.9 mM and a Vmax of 5.96 +/- 0.17 nmol.mg prot-1.0.4 min-1. Uptake of glycyl-L-proline was not significantly inhibited by free amino acids nor by most of the peptides containing D amino acids but was strongly inhibited (up to 64%) by various di- and tripeptides of L amino acids. These results clearly show that glycyl-L-proline was transported by a Na+-independent, carrier-mediated process. Our results suggest that the nonhydrolyzable peptides are transported mostly by carrier-mediated processes in contrast to hydrolyzable peptides.