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.
Research Article| April 01 1990
Characterization of peptide fluxes into human erythrocytes. A proton-n.m.r. study
J E Odoom;
I D Campbell;
J C Ellory;
Biochem J (1990) 267 (1): 141–147.
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J E Odoom, I D Campbell, J C Ellory, G F King; Characterization of peptide fluxes into human erythrocytes. A proton-n.m.r. study. Biochem J 1 April 1990; 267 (1): 141–147. doi: https://doi.org/10.1042/bj2670141
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