Valinomycin, like the
antibiotic gramicidin, interferes with the
ionic
permeability of cell
membranes. But unlike
gramicidin, it acts as a
carrier: imagine an u-shaped molecule on one side of the
cell membrane that carries the ion in its pocket to the other side by flipping 180 degrees, a sort of n-shape, and has the opening at the other side of the membrane. But if you prefer, you may think of a donut with a K
+ in the hole in the middle. Either way, this
ion transport is messing up the
oxidative phosphorylation in
mitochondria and they're using the energy (generated by
electron transport) to accumulate
K+ instead of making energy in the form of
ATP, aka the micro-organism will
die because of lack of sufficient energy.
The
structure of Valinomycin is a repeating cyclic
molecule with four types of residues, being L-
lactate, L-
valine, D-hydroxyisovalerate and D-
valine. It is a
ionophore, with a
hydrophilic centre an a
hydrophobic surface, which is necessary to reside in the lipid bilayer.
The
effectivity of a bit of valinomycin: with a concentration of 10
-7 M, the
conductance of the membrane to K
+ increases more than 10
4-fold. However, this is also
temperature dependent: at lower temperatures (lower than around 35° C.) the membrane is less flexible and the carrier will have more difficulties
flipping from one side to the other. Second remark is, that this activity of valinomycin and the like affect prokaryotes as well as eukaryotes.
Related to the strucutre, is its
preference for K
+ comparing to Na
+ which is a 1000-fold higher, although the
complex is almost the same for both. This is because it is energetically more costly to bind Na
+; or put in another way, water likes Na
+ more than K
+, so "K
+ is allowed to leave" the water-solution.