Ionophore

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Carrier ionophores

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:

  1. 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
  2. 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

Mechanism of action[edit]

Transmembrane ion concentration gradients (Membrane potential) is required for the proper functioning and survival of microorganisms. Ionophores disrupt the membrane potential by conducting ions through a lipid membrane in the absence of a protein pore, and thus could exhibit 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]

The structure of the complex of sodium (Na+) and the antibiotic monensin-A

Synthetic ionophores[edit]

Structure of a potassium complex of a crown ether, a synthetic ionophore-ion complex

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:

See also[edit]

  • Siderophore - Fe3+ binding compounds, found in microbes and grasses

References[edit]

  1. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "Ionophore".
  2. ^ "Ionophores - MeSH Result". 
  3. ^ a b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0080379419. 
  4. ^ 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
  5. ^ 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]