Analysis of the peptide carrier in the scutellum of barley embryos by photoaffinity labelling.

The preparation of a phenylalanine analogue containing an azido group and its incorporation into dipeptides is described. Peptides modified in this way are taken up into barley (Hordeum vulgare L.) scutella via the previously characterized peptide-transport system. Photoactivation of modified peptides in the presence of isolated scutella resulted in irreversible inhibition of peptide uptake in a concentration-dependent manner. Transport of other solutes which share a common mechanism of energy coupling, but which are transported via distinct carriers, was not inhibited after photo-derivatization of scutella with the modified peptides. Derivatization of isolated scutellar tissue with a (14)C-labelled peptide analogue, resulted in incorporation of label into two proteins of Mr = 54000 and 41000. Scutellar tissue from early-germinating seeds, which do not show active peptide uptake, did not incorporate label into these polypeptides. It is concluded that these proteins are components of the barley peptide-transport system.