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2.B.1 The Valinomycin Carrier (Valinomycin) Family

Valinomycin is an ionophoric antibiotic that functions as a carrier to shuttle K+ across a biological membrane, down its electrochemical gradient, thereby eliminating the membrane potential and the K+ concentration gradient. It is synthesized by Streptomyces fulrissimus and contains in sequence: D-valine, L-lactate, L-valine, and D-hydroxy isovalerate repeated three times. It is extremely selective for K+ and renders both artificial and biological membranes permeable to this cation. The valinomycin-K+ complex shields the hydrophilic groups of valinomycin on the interior of the complex when K+ is bound and leaves the hydrophobic rich chains on the external surface exposed to the membrane phospholipid side chains.

The generalized reaction normally catalyzed by valinomycin is:

K+ (out) K+ (in).

That for anionophoric valinomycin derivatives is:

anion (out) ⇌ anion (in).

Berezin 2015 used theory and modeling to investigate K+ valinomycin (Vln) carrier as a classical anionophore. This author discussed formation of the ion pair Vln:K+ or Vln:Cl- versus encapsulation of the anion into a Vln:Cl- complex as two alternative mechanisms that could account for high anionophoretic activity of the cyclic peptide (Riddell and Zhou 1994).  Constructing kinetic models helped distinguish between the two (Berezin 2015).

References associated with 2.B.1 family:

Andersson, M.A., R. Mikkola, R.M. Kroppenstedt, F.A. Rainey, J. Peltola, J. Helin, K. Sivonen and M.S. Salkinoja-Salonen (1998). The mitochondrial toxin produced by Streptomyces griseus strains isolated from an indoor environment is valinomycin. Appl. Environ. Microbiol. 64: 4767-4773. 9835560
Berezin, S.K. (2015). Valinomycin as a Classical Anionophore: Mechanism and Ion Selectivity. J. Membr. Biol. 248: 713-726. 25736817
Riddell, F.G. and Z. Zhou. (1994). Mn2+ as a contrast reagent for NMR studies of 35Cl- and 81Br- transport through model biological membranes. J Inorg Biochem 55: 279-293. 7964715
Zubay G. (1993). Biochemistry, Wm. C. Brown Pub., third edition, 954-955.