Uptake of [14C]-Labeled Tri-, Tetra-, and Pentapeptides of Phenylalanine and Glycine by Escherichia coli

Abstract Three radioactively labeled peptides, Phe-[14C]-Gly-Gly, Phe-Gly-[14C]-Gly-Gly, and Phe-Gly-Gly-[14C]-Gly-Gly were synthesized by a solid phase technique and were purified by preparative paper chromatography. In Escherichia coli the relative rates of uptake, at peptide concentrations of 0.1 mm and at 1.0 mm, were inversely proportional to the number of residues in each peptide. The pentapeptide Phe-Gly-Gly-[14C]-Gly-Gly was taken up much more slowly than the homologous tri- and tetrapeptide. This was interpreted as direct demonstration of a size limit for oligopeptide transport by E. coli. In competition experiments, phenylalanine uptake by E. coli was inhibited by Phe-Gly and Phe-Gly-Gly. Inhibition of Phe-[14C]-Gly-Gly uptake by several peptides indicated a common uptake pathway for small oligopeptides.