Which of the following is an ionophore:

Ans. B. Valinomycinlonophores are ion carrier molecules. They are lipid soluble substances, capable of binding and carrying specific cations (other than H+) through the mitochondrial membrane. Oxidative phosphorylation can be prevented by certain ionophores. They differ from uncoupling agents in that they promote the transport of other cations through the membrane. For e.g. The toxic antibiotic Valinomycin allows penetration of K+ through the mitochondrial membrane, discharging the membrane potential across inner membrane. Gramicidin also acts as an ionophore for K+ and Na+ thus abolishing pH gradient, inhibiting phosphorylation.