THE INTERACTION OF PHTHALOCYANINE WITH PLANAR LIPID BILAYERS - PHOTODYNAMIC INACTIVATION OF GRAMICIDIN CHANNELS

The effect of phthalocyanines, the potent photodynamic sensitizers, on the electric properties of the bilayer lipid membrane (BLM) is studie d. It is shown, that tetrasulfonated, as well as trisulfonated, alumin ium phthalocyanine do not alter the conductance of BLM, but elicit cer tain changes in the boundary potential difference, which points in fav or of dye adsorption on BLM. Under the conditions of intense visible l ight irradiation, the phthalocyanines cause an increase in the conduct ance, resulting in the irreversible breakdown of BLM, formed from soy bean phosphatidylcholine, but fail to change the conductance of BLM, f ormed from diphytanoilphosphatidylcholine. The phthalocyanine-sensitiz ed inactivation of gramicidin channels incorporated into BLM is observ ed under the conditions of weak visible light irradiation using an He- Ne laser. The photodynamic blockage of model ionic channels is conside rably suppressed after oxygen depletion. The phenomenon consists of a marked reduction of a number of open channels, probably due to photomo dification of tryptophan residues, essential for gramicidin functionin g. The mechanism of the channel inactivation, involving the photosensi tized reaction of the II type, and the relevance to the interaction of sensitizers with biomembranes, is discussed.