title: Stereospecificity of peptide transport by germinating barley embryos.
abstract: The stereospecific requirements for peptide transport in the scutellum of germinating barley (Hordeum vulgare) embryos are described. Replacement of an L-amino acid residue in a peptide by its D-stereoisomer decreases the affinity of the peptide for the transport site, leading to a reduction in transport. Substitution of a second D-residue reduces affinity still further. The extent to which transport is inhibited depends upon the position of the D-residue in the primary sequence, with D-residues at the C-terminus of the peptide having the greatest effect. Competition between D- and L-peptides indicates that they both enter via the same transport system. Although D-amino acids can be accumulated when presented as a peptide, these same D-residues are not transported when supplied as the free amino acids. L-Leu-D-leu is accumulated intact against a concentration gradient, indicating the operation of an active transport mechanism that can function without the involvement of peptidase activity.
authors.affiliation: Department of Botany, Science Laboratories, University of Durham, South Road, DH1 3LE, Durham, UK.
authors.forename: C F
authors.initials: CF
authors.lastname: Higgins
authors.forename: J W
authors.initials: JW
authors.lastname: Payne