Evidence for a single common carrier for uptake of a dipeptide and a tripeptide by hamster jejunum in vitro

This paper describes an investigation of whether a dipeptide and a tripeptide were taken up by hamster jejunum by the same transport system, or whether there was evidence of uptake by more than one transport system. The work was carried out with rings of everted hamster jejunum in vitro, under conditions of influx, using the "model" peptides glycylsarcosine, glycylsarcosylsarcosine, and glycylsarcosylsarcosylsarcosine. These peptides are all exceptionally resistant to hydrolysis, appearing intact in the rings, and the di- and tripeptide have previously been shown to be concentrated in the rings by active transport. The results showed that influx of glycylsarcosine was inhibited by glycylsarcosylsarcosine in a competitive way, and that each of the peptides was capable of causing virtually complete inhibition of influx of the other. Glycylsarcosylsarcosylsarcosine had no effect on influx of glycylsarcosine or of glycylsarcosylsarcosine. It was concluded that although the existence of multiple transport systems shared by both glycylsarcosine and glycylsarcosylsarcosine could not be ruled out, the simplest hypothesis was that both the dipeptide and the tripeptide shared a single common carrier for uptake. The tetrapeptide glycylsarcosylsarcosylsarcosine was apparently not transported by this carrier, in agreement with previous results. The possible effects of the "unstirred layer" were taken into account in considering the results and are discussed. They do not alter the conclusions reached.