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An ionophore is a lipid-soluble molecule usually synthesized by microorganisms to transport ions across the lipid bilayer of the cell membrane. There are two broad classifications of ionophores.
- Small molecules (mobile ion carriers) that bind to a particular ion, shielding its charge from the surrounding environment, and thus facilitating its crossing of the hydrophobic interior of the lipid membrane.
- Channel formers that introduce a hydrophilic pore into the membrane, allowing ions to pass through while avoiding contact with the membrane's hydrophobic interior.
Ionophores disrupt transmembrane ion concentration gradients, required for the proper functioning and survival of microorganisms, and thus have antibiotic properties. They are produced naturally by certain microbes and act as a defense against competing microbes.
In laboratory research, ionophores are used to increase the permeability of biological membranes to certain ions. Additionally, some ionophores are used as antibiotics and/or as growth enhancing feed additives for certain food animals such as cattle (see monensin). The U.S. Department of Agriculture sent a letter to Tyson Foods to remove labels for chickens that said "raised without antibiotics" because of the use of ionophores in their feed.[1]
Representative ionophores (with the ion(s) they act upon):
- 2,4-Dinitrophenol (H+)
- Beauvericin (Ca2+, Ba2+)
- Calixarene
- Calcimycine (A23187)
- Carbonyl cyanide m-chlorophenyl hydrazone
- Crown ether
- FCCP or Carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (H+)
- Gramicidin A (H+, Na+, K+)
- Ionomycin (Ca2+)
- Lasalocid
- Monensin (Na+, H+)
- Nigericin (K+, H+, Pb2+)
- Nonactin (Ammonium ionophore I)
- Nystatin
- Proton ionophore II (4-Nonadecylpyridine)
- Proton ionophore III (N,N-Dioctadecylmethylamine)
- Salinomycin (K+)
- Valinomycin (K+)
References
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