Ionophore
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.
- Chemical compounds (mobile ion carriers) that bind to a particular ion,[1] shielding its charge from the surrounding environment, and thus facilitating its crossing of the hydrophobic interior of the lipid membrane.
- Channel formers[2] that introduce a hydrophilic pore into the membrane, allowing ions to pass through while avoiding contact with the membrane's hydrophobic interior.
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[edit] Mechanism of action
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 a variety of microbes and act as a defense against competing microbes. Many antibiotics, particularly the macrolide antibiotics, are ionophores that exhibit high affinities for Na+ or K+.[3] The structure of the sodium and potassium complexes of antibiotics have been repeatedly verified by X-ray crystallography.[4]
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 feed animals such as cattle (see monensin).[5]
[edit] Synthetic ionophores
Most prominent synthetic ionophores are those based on crown ethers, cryptands, and calixarenes. These synthetic species are often macrocyclic.[3] Some synthetic agents are not macrocyclic, e.g., Carbonyl cyanide-p-trifluoromethoxyphenylhydrazone. Even simple organic compounds, such as phenols, exhibit ionophoric properties.
[edit] Appendix: list of representative biological ionophores
With the ion(s) they act upon:
- A23187 (Ca2+)
- Beauvericin (Ca2+, Ba2+)
- Calcimycine (A23187)
- Enniatin (Ammonium)
- Gramicidin A (H+, Na+, K+)
- Ionomycin (Ca2+)
- Lasalocid
- Monensin (Na+, H+)
- Nigericin (K+, H+, Pb2+)
- Nonactin (Ammonium ionophore I)
- Nystatin
- Salinomycin (K+)
- Valinomycin (Potassium ionophore I)
[edit] See also
- Siderophore - Fe2+ binding compounds, found in microbes and grasses.
[edit] References
- ^ Nic, M.; Jirat, J.; Kosata, B., eds. (2006–). "Ionophore". IUPAC Compendium of Chemical Terminology (Online ed.). doi:10.1351/goldbook.IT06772. ISBN 0-9678550-9-8. http://goldbook.iupac.org/IT06772.html.
- ^ "Ionophores - MeSH Result". http://www.ncbi.nlm.nih.gov/sites/entrez?Db=mesh&Cmd=ShowDetailView&TermToSearch=68007476&ordinalpos=1&itool=EntrezSystem2.PEntrez.Mesh.Mesh_ResultsPanel.Mesh_RVDocSum.
- ^ a b Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0080379419.
- ^ L. K. Steinrauf, J. A. Hamilton, M. N. Sabesan "Crystal structure of valinomycin-sodium picrate. Anion effects on valinomycin-cation complexes" J. Am. Chem. Soc. 1982, Volume 104, pp 4085–4091. doi:10.1021/ja00379a008
- ^ 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. Kabel, Marcus; Christine Simmons (2007-11-20). "USDA Revokes OK for Tyson Chicken Labels". http://ap.google.com/article/ALeqM5iYfYJmjwYMb-6RiqjCbJ481k5xjgD8T16P5O0. Retrieved 2007-11-20.
[edit] External links
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