Characterization of peptide fluxes into human erythrocytes. A proton-n.m.r. study.
A new protocol for measuring cellular uptake of dipeptides was developed in which the problem of peptide hydrolysis is obviated by introduction into the cell suspension of a membrane-permeant peptidase inhibitor. The uptake of unlabelled dipeptide is readily monitored so long as some analytical technique is available for measuring the intracellular peptide concentration; in this study we used n.m.r. spectroscopy. Using this protocol, we demonstrated that dipeptide uptake by human erythrocytes occurs by simple diffusion through the lipid bilayer and not via a high-capacity protein-mediated transport system. Substantiating evidence includes demonstration that: (a) the fluxes are slow compared with known protein-mediated transport processes in human erythrocytes; (b) the uptake is not stereospecific; (c) the uptake does not display saturation kinetics; (d) the fluxes are significantly enhanced by butanol; (e) a distinct correlation exists between the size-corrected permeability coefficients of the dipeptides and their calculated n-octanol/water partition coefficients. It is calculated that under normal physiological conditions the diffusive fluxes of circulating plasma peptides into human erythrocytes are too small for these cells to play a significant role in dipeptide catabolism.
Odoom
J E
JE
Department of Biochemistry, University of Oxford, U.K.
Campbell
I D
ID
Ellory
J C
JC
King
G F
GF
D000900:Anti-Bacterial Agents; D002463:Cell Membrane Permeability; D004058:Diffusion; D004150:Dipeptidases / Q000037:antagonists & inhibitors / Q000097:blood; D004151:Dipeptides / Q000097:blood*; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D007930:Leucine / Q000031:analogs & derivatives / Q000494:pharmacology; D008051:Lipid Bilayers / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D009842:Oligopeptides / Q000494:pharmacology; D010455:Peptides
D000900:Anti-Bacterial Agents; D004151:Dipeptides; D008051:Lipid Bilayers; D009842:Oligopeptides; D010455:Peptides; C016977:amastatin; D004150:Dipeptidases; C038937:dipeptidase; D007930:Leucine; C012211:ubenimex