THE EFFECT OF FREE-RADICALS ON THE CONDUCTANCE INDUCED BY ALAMETHICININ PLANAR LIPID-MEMBRANES - ACTIVATION AND INACTIVATION

Exposure to ionizing radiation of planar lipid membranes doped with al amethicin gives rise to an increase and to a subsequent decrease of th e membrane conductance. Both effects are due to the presence of radiat ion-induced free radicals of water radiolysis as was shown by addition of various radical scavengers. The increase of the conductance was fo und to be a consequence of free radical-initiated lipid peroxidation f avouring the formation of active ion channels. The decrease of the con ductance observed at larger radiation doses is due to an inactivation of alamethicin monomers. The characteristic D-37 dose of inactivation was found to be about two orders of magnitude larger than in the case of gramicidin A. The comparatively high sensitivity of the latter is d ue to the presence of its four tryptophan residues. Inactivation of tr ichorzianine AIIIc, an analogue of alamethicin with a C-terminal trypt ophanol residue, occurs at radiation doses two orders of magnitude low er than observed with alamethicin.