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Valinomycin

Valinomycin

Molecular formula	C₅₄H₉₀N₆O₁₈
Identifiers
CAS number	2001-95-8
Properties
Molar mass	1111.32
Appearance	White solid
Melting point	172°C -177 °C
Solubility	Methanol, Ethanol, Ethyl acetate, Petrol-ether, Dichloromethane
λ_max	220 nm
Hazards
Main hazards	Neurotoxicant
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Valinomycin is a dodecadepsipeptide, that is, it is made of twelve alternating amino acids and esters to form a macrocyclic molecule.

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Valinomycin is obtained from the cells of several Streptomyces strains, one of them Str. Tsusimaensis.

It is a member of the group of natural neutral ionophores because it doesn't have a residual charge. It consists of enantiomeres D- and L-Valine, D-Hydroxyvaleric acid and L-Lactic acid. Structures are alternated bound via amide and ester bridges. Valinomycin is highly selective for potassium ions over sodium ions within the cell membrane.^[1] It functions as a potassium-specific transporter and facilitates the movement of potassium ions through lipid membranes "down" an electrochemical potential gradient.^[2] The stability constant K for the potassium-valinomycin complex is 10⁶ and for the sodium-valinomycin complex only 10. This difference is important for maintaining the selectivity of valinomycin for the transport of potassium ions (and not sodium ions) in biological systems.

Structure

From the chemical structure it can be seen that there are some prevailing features. The 12 carbonyl groups are essential for the binding of metal ions, and also for solvation in polar solvent. The isopropyl groups and methyl groups are responsible for solvation in nonpolar solvents. ^[3] Along with its shape and size this molecular duality is the main reason for its binding properties. For polar solvents valinomycin will mainly expose the carbonyls to the solvent and in nonpolar solvents the iso-propyl groups are located predominantly on the exterior of the molecule. This conformation changes when valinomycin is bound to a potassium ion. The molecule is "locked" into a conformation where the exterior is made up of the isopropyl groups. It is not actually locked into configuration because the size of the molecule makes it highly flexible, but the potassium gives some degree of coordination to the macromolecule.

Application

Valinomycin acts as ion-exchange agent in Potassium selective electrode.^[4]

References

^ Rose Lars and Jenkins ATA (2007). "The effect of the ionophore valinomycin on biomimetic solid supported lipid DPPTE/EPC membranes". Bioelectrochem. 70 (2): 387-393. Entrez PubMed 16875886
^ Cammann K (1985). "Ion-selective bulk membranes as models". Top. Curr. Chem. 128: 219-258.
^ Thompson M and Krull UJ (1982). "The electroanalytical response of the bilayer lipid membrane to valinomycin: membrane cholesterol content". Anal. Chim. Acta 141: 33-47.
^ Safiulina D, Veksler V, Zharkovsky A and Kaasik A (2006). "Loss of mitochondrial membrane potential is associated with increase in mitochondrial volume: physiological role in neurones". J Cell Physiol 206 (2): 347-353. Entrez PubMed 16110491

Category: Biomolecules

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Valinomycin". A list of authors is available in Wikipedia.