keep cells healthy
Because the health of cells depends on maintaining the proper levels of cations in intracellular fluids, any change that affects the normal flux of metal ions across cell membranes could well cause an organism to die. Molecules that facilitate the transport of metal ions across membranes are generally called ionophores ionplus phore from the Greek phorein, meaning to carry . Many ionophores are potent antibiotics that can kill or inhibit the growth of bacteria. An example isvalinomycin, a cyclic molecule with a central cavity lined with oxygen atoms part a in Figure 21.14 "Valinomycin Is an Antibiotic That Functions Like an Ionophore" that is similar to the cavity of a crown ether part a in Figure 13.7 "Crown Ethers and Cryptands" . Like a crown ether, valinomycin is highly selective: its affinity for K+ is about 1000 times greater than that for Na+. By increasing the flux of K+ ions into cells, valinomycin disrupts the normal K+ gradient across a cell membrane, thereby killing the cell part b in Figure 21.14 "Valinomycin Is an Antibiotic That Functions Like an Ionophore" . Figure 21.14 Valinomycin Is an Antibiotic That Functions Like an Ionophore.