TEMPERATURE-INDUCED CHANGES IN FLUORESCENCE PROPERTIES AS A PROBE OF PORPHYRIN MICROENVIRONMENT IN LIPID-MEMBRANES .2. THE PARTITION OF HEMATOPORPHYRIN AND PROTOPORPHYRIN IN MITOCHONDRIA
F. Ricchelli et al., TEMPERATURE-INDUCED CHANGES IN FLUORESCENCE PROPERTIES AS A PROBE OF PORPHYRIN MICROENVIRONMENT IN LIPID-MEMBRANES .2. THE PARTITION OF HEMATOPORPHYRIN AND PROTOPORPHYRIN IN MITOCHONDRIA, European journal of biochemistry, 233(1), 1995, pp. 165-170
The temperature dependence of hematoporphyrin and protoporphyrin fluor
escence quantum yields (Phi(F)) was studied after delivery to whole mi
tochondria or isolated inner (IMM) and outer (OMM) mitochondrial membr
anes, obtained from liver of Wistar rats. These studies are very sensi
tive to variations of the porphyrin lipid environment. Before incorpor
ation, the polphyrins were dissolved in 0.01 M sodium phosphate, 0.15
M NaCl, pH 7.4) NaCl/P-i (only hematoporphyrin) or dispersed into lipo
somes of dipalmitoylphosphoglycerocholine (Pam(2)GroPCho), sometimes e
nriched with cholesterol or cardiolipin. Whole mitochondria show highe
r incorporation capacity of hematoporphyrin and protoporphyrin than is
olated IMM and OMM, probably because additional, energy-sensitive tran
sport mechanisms for the porphyrin uptake occur in intact organelles.
A small decrease in protoporphyrin uptake is observed in OMM in compar
ison with IMM; in contrast, the decrease in hematoporphyrin uptake by
OMM is rather significant. A comparison between the results obtained w
ith IMM, OMM and whole mitochondria show that both porphyrins, when re
leased to the intact organelles, preferentially localize in the IMM, i
rrespective of the lipid carrier used. NaCl/P-i-dissolved hematoporphy
rin probably interacts with some membrane proteins, due to the similar
ity of the Arrhenius plots with those obtained fbr liposome-entrapped
human serum albumin/hematoporphyrin complexes which were used as model
s to mimic hematoporphyrin-membrane protein binding sites. Liposomal h
ematoporphyrin and protoporphyrin bind to lipid domains. Hematoporphyr
in accumulates in specific, localized lipid regions, perhaps in the bo
undary lipids area surrounding some inner-mitochondrial carriers; prot
oporphyrin accomodates in more rigid, lipid areas. On these bases, the
higher photoactivity of hematoporphyrin, previously observed in mitoc
hondria, in comparison with protoporphyrin, can be easily explained. F
ormation of linear dimers/aggregates, endowed with higher Phi(F) than
that of the monomers, are postulated to occur for both porphyrins only
in the inner mitochondrial membrane.