A radioisotope incorporation method for studying the transport and utilization of peptides byEscherichia coli

Most microorganisms utilize peptide~ nutritionally at sotnces of amino acids for protein synthesis [ l-4].In Escherkq~ coli, which lacks extracellular peptidases, peptides are tra.,nportedintact and hydrolysed intracellularly.Present ideas on the peptide permeases of E. coil derive mainly from experiments in which amino acid auxotroph$ have been grow, on defined peptides [I-6].However, this indirect way of studying transport is of limited melulneu in that it requires long incubation periods [8-20 hJ and relatively large amounts of peptide$ to produce measurable growth resonances."I]fis paper d~:ribea a new approach, using radioactive amino acids, that allows a rapid and sensitive study to be made of peptide transport and utilization, and in addition, provides peptide binding affmities for the transport systems.A preliminary account of some of this material has been presented