From Big Medical Encyclopedia

IONOPHORES — the substances connecting various ions in solutions and giving to biological or artificial membranes property of permeability in relation to a trapped ion. The term «ionophore» was offered in 1967 for group of the substances promoting transfer of alkali metals through membranes when their ability to form specific complexes with the transported cations was open.

K I. many substances belong: antibiotics valinomitsin, nigeritsin, monensin, A 23187, X — 537A, enniatina, naktina, gramicidins A, B and C, a row related to them antibiotics and their synthetic analogs, and also many macrocyclic and macrobicyclic polyethers. Properties I. are found in the polypeptides received at the proteolysis, which are carrying out transport of ions in cells (metallzavisimy ATP-ases of bacteria and a sarcoplasmic reticulum, a squirrel of excitable membranes etc.). It is supposed that prostaglandins (see)

I. I. also are show the action at very low concentrations (10 - 11 - 10 - 6 L), have sharp ionic selectivity. E.g., valinomitsin transfers potassium ions to 10 thousand times more actively, than ions of sodium, a naktina find high ammonium specificity, monensin is selective in relation to ions of sodium, and A 23187 is the best And. for calcium ions.

Mechanism of action And. includes several stages. In the beginning the transported ion interacts with And., being on a surface of a membrane. At the same time the ion in whole or in part loses the hydrated cover, is implemented into a molecular cavity And. also keeps due to interaction with polar groups of IONOPHORES there. Stability and other properties of the formed complex are defined by features of its space organization. E.g., hydrocarbon radicals And. are located on a surface of a complex and provide its lipophilicity, i.e. ability to enter lipidic zones of membranes. The sizes of a molecular cavity precisely correspond to diameter of the connected ion. Under the influence of an electrochemical gradient the ion as a part of a complex passes through a membrane and is released on the opposite side.

Scheme of mechanisms of action of ionophores: 1 — «the mechanism of a carrier» — the ionophore connects an ion (M +) and moves it through a membrane; 2 — «the channel mechanism» — the ionophores which are built in a membrane form «channel» on which ions pass through a membrane., Shooters specified the direction of movement of ions.

On the mechanism of action And. divide into two groups (fig.): carry to the first And., which move together with a trapped ion («the mechanism of a carrier»); to the second — And., built in a membrane in such a way that form «channel», lengthways to-rogo non freely moves through a membrane («the channel mechanism»). Typical representatives And. the first group are valinomitsin and naktina, and the second — gramicidins A, B and

S. I. apply in chemical technology to extraction and division of rare metals, to creation of new catalysts, and in instrument making — to creation of highly effective ionizbiratelny sensors. In particular, the electrodes made on the basis of a valinomitsin are used for determination of level of potassium in biol, objects (in blood, cells etc.). With their help it is possible to activate or suppress these or those fermental systems, to regulate the size of electric membrane potential, to influence transport of protons, neutral substances and anions, and also intracellular osmotic pressure etc.

With the help And. it is possible to study from essentially new positions mechanisms of intracellular permeability and influence of various factors (e.g., toxicants) on a condition of internal environment of an organism. Discovery of substances of a class I. promoted deeper studying of the mechanism of action of antibiotics, allowed to make synthesis of new antibiotics with the set properties and their selection for medical practice.

High biol, activity And. gives the chance to apply them as pharmaceuticals. So, polyester And. were an effective remedy for removal of harmful metals from an organism. Valinomitsin is capable to reduce intraocular pressure at glaucoma, lazalotsid — to stimulate cordial activity etc. Opportunities of practical use of ionophores are not exhausted, and it is necessary to expect further expansion of the sphere of their use in various fields of science, the equipment and medicine.

See also Antibiotics , Ions , Membranes biological , Permeability , Transport of ions .

Bibliography: Ovchinnikov Yu. A., Ivanov B. T. and A. M. Membrano-aktivnye's Shkrob complexons, M., 1974, bibliogr.: Pressman B. C. Biological applications of ionophores, Ann. Rev. Biochem., v. 45, p. 501, 1976, bibliogr.

V. T. Ivanov.