title: Characterization of a transport activity for long-chain peptides in barley mesophyll vacuoles.
abstract: The plant vacuole is the largest compartment in a fully expanded plant cell. While only very limited metabolic activity can be observed within the vacuole, the majority of the hydrolytic activities, including proteolytic activities reside in this organelle. Since it is assumed that protein degradation by the proteasome results in the production of peptides with a size of 3-30 amino acids, we were interested to show whether the tonoplast exhibits a transport activity, which could deliver these peptides into the vacuole for final degradation. It is shown here that isolated barley mesophyll vacuoles take up peptides of 9-27 amino acids in a strictly ATP-dependent manner. Uptake is inhibited by vanadate, but not by NH(+)(4), while GTP could partially substitute for ATP. The apparent affinity for the 9 amino acid peptide was 15 μM, suggesting that peptides are efficiently transferred to the vacuole in vivo. Inhibition experiments showed that peptides with a chain length below 10 amino acids did not compete as efficiently as longer peptides for the uptake of the 9 amino acid peptide. Our results suggest that vacuoles contain at least one peptide transporter that belongs to the ABC-type transporters, which efficiently exports long-chain peptides from the cytosol into the vacuole for final degradation.
authors.affiliation: Institute of Plant Biology, University Zurich, Zollikerstrasse 107, 8008 Zurich, Switzerland.
authors.forename: Magali Schnell
authors.initials: MS
authors.lastname: Ramos
authors.forename: Rupert
authors.initials: R
authors.lastname: Abele
authors.forename: Réka
authors.initials: R
authors.lastname: Nagy
authors.forename: Marianne Suter
authors.initials: MS
authors.lastname: Grotemeyer
authors.forename: Robert
authors.initials: R
authors.lastname: Tampé
authors.forename: Doris
authors.initials: D
authors.lastname: Rentsch
authors.forename: Enrico
authors.initials: E
authors.lastname: Martinoia
mesh_terms: D001692:Biological Transport; D001467:Hordeum / Q000737:chemistry / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D058503:Mesophyll Cells / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism*; D010455:Peptides / Q000737:chemistry / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism; D014617:Vacuoles / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism*
chemical_list: D010455:Peptides; D010940:Plant Proteins