Ionophore properties of cationomycin in large unilamellar vesicles studied by 23Na- and 39K-NMR.

Cationomycin, isolated from Actinomadura azurea belongs to a large family of carboxylic polyether antibiotics, transporting monovalent cations through membranes by a mobile carrier mechanism, leading globally to an H+, M+ exchange. In this report the cation transporting properties of cationomycin were characterized in large unilamellar vesicles (LUVs) by 23Na- and 39K-NMR. Kinetic studies showed that cationomycin transported potassium more rapidly than sodium, and the more stable complex was formed with potassium at the water/membrane interface. The transport rate constants measured for cationomycin were compared with those obtained for monensin. Cationomycin transports Na+ more slowly than monensin and has a lower stability complex with Na+ because of the lower formation rate for the complex on the membrane surface. Our results show that transport selectivity of cationomycin is in favour of K+ versus Na+ while the reverse situation is observed for monensin. The relationships between the ionophore properties of cationomycin and monensin with their biological activities are discussed.