Ionophore
An ionophore is a lipid-soluble molecule usually synthesized by microorganisms to transport ions across the lipid bilayer of the cell membrane. The two broad classifications of ionophores are:
- 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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Mechanism of action[edit]
Ionophores disrupt the 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]
Synthetic ionophores[edit]
Most prominent synthetic ionophores are 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.
List of representative biological ionophores[edit]
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)
See also[edit]
- Siderophore - Fe3+ binding compounds, found in microbes and grasses
References[edit]
- ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "Ionophore".
- ^ "Ionophores - MeSH Result".
- ^ a b Greenwood, Norman N.; Earnshaw, Alan (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 US 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". Retrieved 2007-11-20.[dead link]
External links[edit]
- Fluka ionophores for ion-selective electrodes
- Medical Information database Reference.MD
- Structures and Properties of Naturally Occurring Polyether Antibiotics, J. Rutkowski, B. Brzezinski; open access review article
- Polyether ionophores—promising bioactive molecules for cancer therapy, A. Huczyński; open access review article
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