Evidence for chloramphenicol/H+ antiport in Cmr (MdfA) system of Escherichia coli and properties of the antiporter

J Biochem. 1998 Jul;124(1):187-93. doi: 10.1093/oxfordjournals.jbchem.a022078.


We detected chloramphenicol/H+ antiport activity in membrane vesicles of Escherichia coli and cloned a gene for the antiporter from chromosomal DNA of E. coli. Introduction of the gene into E. coli cells conferred resistance to chloramphenicol and ethidium. A slight increase in resistance to acridine orange was also observed. Elevated chloramphenicol efflux and ethidium efflux were observed in cells harboring a plasmid carrying the gene. Addition of chloramphenicol to the assay mixture reduced the efflux of ethidium. Elevated chloramphenicol/H+ antiport activity was observed in membrane vesicles prepared from cells harboring the plasmid. The pH optimum for the activity was 6.5. We sequenced the gene and deduced the amino acid sequence of its product. A sequence homology search revealed that it was same as that of Cmr (or MdfA). Thus, it became clear that Cmr (MdfA) is the chloramphenicol(and ethidium)/H+ antiporter.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins*
  • Biological Transport
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Chloramphenicol / metabolism*
  • Cloning, Molecular
  • Escherichia coli / metabolism*
  • Escherichia coli Proteins*
  • Ethidium / metabolism
  • Hydrogen-Ion Concentration
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Membrane Transport Proteins*
  • Protons


  • Bacterial Proteins
  • Carrier Proteins
  • Escherichia coli Proteins
  • Mdfa protein, E coli
  • Membrane Proteins
  • Membrane Transport Proteins
  • Protons
  • Chloramphenicol
  • Ethidium