Influence of proton and essential histidyl residues on the transport kinetics of the H+/peptide cotransport systems in intestine (PEPT 1) and kidney (PEPT 2)

Biochim Biophys Acta. 1997 Mar 13;1324(2):251-62. doi: 10.1016/s0005-2736(96)00231-3.


The mechanism by which H+ alters the kinetics of the H+-coupled peptide transporters PEPT 1 and PEPT 2 was investigated in two different cell lines which differentially express these transporters, namely Caco-2 cells (PEPT 1) and SKPT cells (PEPT 2). The effects of H+ on the affinity and the maximal velocity of Gly-Sar uptake were analyzed in these cells under identical conditions. In both cells, H+ influenced only the maximal velocity of uptake and not the apparent affinity. The effects of H+ on the IC50 values (i.e., concentration necessary to cause 50% inhibition) of the cationic dipeptide Ala-Lys and the anionic dipeptide Ala-Asp for inhibition of Gly-Sar uptake were also investigated. H+ did not change the IC50 value for Ala-Lys but did decrease the IC50 value for Ala-Asp considerably. The influence of diethylpyrocarbonate (DEP) on the kinetic parameters of PEPT 1 and PEPT 2 was then studied. Histidyl residues are the most likely amino acid residues involved in H+ binding and translocation in H+-coupled transport systems and DEP is known to chemically modify histidyl residues and block their function. DEP treatment altered the maximal velocity of Gly-Sar uptake but had no effect on its K(t) (Michaelis-Menten constant) or the IC50 values of Ala-Lys or Ala-Asp for the inhibition of Gly-Sar uptake. It is concluded that H+ stimulates PEPT 1 and PEPT 2 primarily by increasing the maximal velocity of the transporters with no detectable influence on the substrate affinity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biological Transport / drug effects
  • Caco-2 Cells / metabolism
  • Carrier Proteins / metabolism*
  • Cell Line
  • Cephalexin / pharmacology
  • Diethyl Pyrocarbonate / pharmacology
  • Dipeptides / metabolism
  • Dipeptides / pharmacology
  • Dose-Response Relationship, Drug
  • Histidine / physiology*
  • Humans
  • Kidney Tubules, Proximal / cytology
  • Kidney Tubules, Proximal / metabolism
  • Kinetics
  • Peptide Transporter 1
  • Protons*
  • Rats
  • Symporters*


  • Carrier Proteins
  • Dipeptides
  • Peptide Transporter 1
  • Protons
  • SLC15A1 protein, human
  • Slc15a1 protein, rat
  • Symporters
  • hydrogen-coupled oligopeptide transporter PepT2
  • alanylaspartic acid
  • glycylsarcosine
  • Histidine
  • Diethyl Pyrocarbonate
  • Cephalexin