F. Ricchelli et al., INTERACTION OF PHTHALOCYANINES WITH LIPID-MEMBRANES - A SPECTROSCOPICAND FUNCTIONAL-STUDY ON ISOLATED RAT-LIVER MITOCHONDRIA, Biochimica et biophysica acta. Biomembranes, 1196(2), 1994, pp. 165-171
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.