INTERACTION OF PHTHALOCYANINES WITH LIPID-MEMBRANES - A SPECTROSCOPICAND FUNCTIONAL-STUDY ON ISOLATED RAT-LIVER MITOCHONDRIA

Absorption and emission spectroscopic studies on Zn(II)-phthalocyanine (ZnPc) incorporated into unilamellar liposomes of dipalmitoylphosphat idylcholine, sometimes added with cholesterol or cardiolipin, and rele ased to rat liver mitochondria via the three types of liposomal vesicl es indicated that: (a) ZnPc predominantly dissolves in all lipid domai ns of biological membranes with the exception of cardiolipin-containin g regions; a partial localization of ZnPc in protein binding sites is also postulated; (b) the spectroscopic properties of ZnPc, although ma inly determined by the aggregation state of the dye, are somewhat infl uenced by the physico-chemical characteristics of the lipid environmen t; (c) ZnPc-binding lipid domains in mitochondria are mainly localized in the outer membrane; this conclusion is clearly deduced from the tr ends of Arrhenius plots of the ZnPc fluorescence quantum yield in whol e mitochondria and isolated inner or outer membrane in the temperature range -10 degrees C- + 45 degrees C; (d) the nature of the ZnPc-bindi ng site in mitochondria is not dependent on the chemical composition o f the liposome carrier, contrary to what observed for other hydrophobi c dyes, such as porphyrins. This has been also confirmed by photosensi tization experiments. Actually, illumination of ZnPc-loaded mitochondr ia by 600-700 nm light causes a decline of the respiratory control rat io, which is essentially dependent on the amount of incorporated photo sensitizer, irrespective of the composition of the carrier.