NMR-STUDY OF ION-TRANSPORT THROUGH PHOSPHOLIPID-BILAYERS MEDIATED BY THE IONOPHORIC ANTIBIOTIC SEPTAMYCIN

The ionophoric antibiotic septamycin is shown to be an efficient trans porter of sodium, potassium and cesium ions through the membranes of e gg yolk phosphatidylcholine vesicles. The rates of transport with sodi um were measured using Na-23 NMR. Compared to other ionophoric antibio tics that transport sodium, septamycin is found to have the slowest as sociation rate and the fastest dissociation rate. It consequently has a very low stability constant for binding Na+ in the membrane surface. Studies of potassium transport showed that such transport occurs, but did not give sufficiently reliable data to allow the measurement of t ransport rates. Sodium/cesium exchange was observed to occur rapidly. A technique is described whereby the rate of transport of cesium ions from one vesicle to another could be measured.