Ionophore

Source: Wikipedia, the free encyclopedia.
Carrier and channel ionophores
(a) Carrier ionophores reversibly bind ions and carry them through cell membranes.
(b) Channel ionophores create channels within cell membranes to facilitate the transport of ions.

In

liposomes).[1]
Structurally, an ionophore contains a hydrophilic center and a hydrophobic portion that interacts with the membrane.

Some ionophores are synthesized by

microorganisms to import ions into their cells. Synthetic ion carriers have also been prepared. Ionophores selective for cations and anions have found many applications in analysis.[2] These compounds have also shown to have various biological effects and a synergistic effect when combined with the ion they bind.[3]

Classification

monensin A
crown ether
, a synthetic ionophore-ion complex

Biological activities of metal ion-binding compounds can be changed in response to the increment of the metal concentration, and based on the latter compounds can be classified as "metal ionophores", "metal chelators" or "metal shuttles".[3] If the biological effect is augmented by increasing the metal concentration, it is classified as a "metal ionophore". If the biological effect is decreased or reversed by increasing the metal concentration, it is classified as a "metal chelator". If the biological effect is not affected by increasing the metal concentration, and the compound-metal complex enters the cell, it is classified as a "metal shuttle". The term ionophore (from Greek ion carrier or ion bearer) was proposed by Berton Pressman in 1967 when he and his colleagues were investigating the antibiotic mechanisms of valinomycin and nigericin.[4]

Many ionophores are produced naturally by a variety of

plants, and act as a defense against competing or pathogenic species. Multiple synthetic membrane-spanning ionophores have also been synthesized.[5]
The two broad classifications of ionophores synthesized by microorganisms are:

Ionophores that transport

siderophores
.

Synthetic ionophores

Many synthetic ionophores are based on crown ethers, cryptands, and calixarenes. Pyrazole-pyridine and bis-pyrazole derivatives have also been synthesized.[9] These synthetic species are often macrocyclic.[10] Some synthetic agents are not macrocyclic, e.g. carbonyl cyanide-p-trifluoromethoxyphenylhydrazone. Even simple organic compounds, such as phenols, exhibit ionophoric properties. The majority of synthetic receptors used in the carrier-based anion-selective electrodes employ transition elements or metalloids as anion carriers, although simple organic urea- and thiourea-based receptors are known.[11]

Mechanism of action

Ionophores are chemical compounds that reversibly bind and transport

liposomes), or liquid polymeric membranes (carrier-based ion selective electrodes).[1] Structurally, an ionophore contains a hydrophilic center and a hydrophobic portion that interacts with the membrane. Ions are bound to the hydrophilic center and form an ionophore-ion complex. The structure of the ionophore-ion complex has been verified by X-ray crystallography.[12]

Chemistry

Several chemical factors affect the ionophore activity.

biological membranes most commonly via passive transport, which is affected by lipophilicity of the ionophore molecule. The increase in lipophilicity of the ionophore-metal complex enhances its permeability through lipophilic membranes. The hydrophobicity and hydrophilicity of the complex also determines whether it will slow down or ease the transport of metal ions into cell compartments. The reduction potential of a metal complex influences its thermodynamic stability and affects its reactivity
. The ability of an ionophore to transfer ions is also affected by the temperature.

Biological properties

Ionophores are widely used in cell physiology experiments and biotechnology as these compounds can effectively perturb gradients of ions across

parasites. Some ionophores have been introduced into medicinal products for dermatological and veterinary use.[16][17] A large amount of research has been directed toward investigating novel antiviral, anti-inflammatory, anti-tumor, antioxidant and neuroprotective properties of different ionophores.[15][18][3]

timber treatment.[31]

macrolides and are widely used antifungal and antileishmanial medications. These drugs act as ionophores by binding to ergosterol in the fungal cell membrane and making it leaky and permeable for K+ and Na+ ions, as a result contributing to fungal cell death.[32]

Carboxylic ionophores, i.e.

ruminants, such as cattle, and chickens, however this use has been mainly restricted because of safety issues.[34][35]

Zinc ionophores have been shown to inhibit replication of various viruses in vitro, including

MERS-CoV,[41] rhinovirus,[36] SARS-CoV-1,[38][41] Zika virus.[44][45]

Ionophore Cations Sources
This is not a complete list of all known ionophores.
The metal ions listed for each ionophore are not exclusive.
Alamethicin[46][47] Ka+, Na+ Trichoderma viride[48]
Beauvericin[49] Ba2+, Ca2+ Beauveria bassiana, Fusarium species
Calcimycin[50][51]
 Mn2+, Ca2+, Mg2+, Sr2+, Ba2+, Zn2+, Co2+, Ni,2+, Fe2+ Streptomyces chartreusensis
Chloroquine[52] Zn2+ Cinchona officinalis
Clioquinol[3] Zn2+, Cu2+, Fe2+ Synthetic ionophore
Diiodohydroxyquinoline[53] Zn2+ Synthetic ionophore
Dithiocarbamates (pyrrolidine dithiocarbamate and other derivatives)[54]
 Zn2+, Cu2+ Synthetic ionophore
Enniatin[55] NH4+ Fusarium species
Epigallocatechin gallate[56] Zn2+ Camellia sinensis, apples, plums, onions, hazelnuts, pecans, carobs
Gramicidin A[57]
 K+, Na+ Brevibacillus brevis
Hinokitiol[58] Zn2+ Cupressaceae species
Ionomycin[59] Ca2+ Streptomyces conglobatus
Laidlomycin[60] Li+, K+, Na+, Mg2+, Ca2+, Sr2+ Streptomyces species
Lasalocid[61] K+, Na+, Ca2+, Mg2+ Streptomyces lasalocidi
Maduramicin[62] K+, Na+ Actinomadura rubra
Monensin[3][63][64] Li+, K+, Na+, Rb+, Ag+, Tl+, Pb2+
Streptomyces cinnamonensis
Narasin[65] K+, Na+, Rb+
Streptomyces aureofaciens
Nigericin[66] K+, Pb2+ Streptomyces hygroscopicus
Nonactin[67][68] K+, Na+, Rb+, Cs+, Tl+, NH4+
Streptomyces chrysomallus, Streptomyces werraensis
Nystatin K+ Streptomyces noursei
PBT2[69] Zn2+, Fe2+, Mn2+, Cu2+ Synthetic analogue of
8-hydroxyquinoline
Pyrazole-pyridine and bis-pyrazole derivatives[70] Cu2+ Synthetic ionophore
Pyrithione[58] Zn2+, Cu2+, Pb2+ Allium stipitatum
Quercetin[71] Zn2+ Widely distributed in nature, found in many vegetables, fruits, berries, herbs, trees and other plants
Salinomycin[72] K+, Na+, Cs+, Sr2+, Ca2+, Mg2+ Streptomyces albus
Semduramicin[73] Na+, Ca2+ Actinomadura roseorufa
Valinomycin[74] K+ Streptomyces species
Zincophorin[3] Zn2+ Streptomyces griseus

See also

References

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External links
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