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

The ionophoric antibiotic septamycin is shown to be an efficient transporter of sodium, potassium and cesium ions through the membranes of egg yolk phosphatidylcholine vesicles. The rates of transport with sodium were measured using Na-23 NMR. Compared to other ionophoric antibiotics that transport sodium, septamycin is found to have the slowest association 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 transport 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.