M. Merchat et al., STUDIES ON THE MECHANISM OF BACTERIA PHOTOSENSITIZATION BY MESOSUBSTITUTED CATIONIC PORPHYRINS, Journal of photochemistry and photobiology.B, Biology, 35(3), 1996, pp. 149-157
Cationic porphyrins have been shown to photoinduce the direct inactiva
tion of Gram-positive (G+) and Gram-negative (G-) bacteria, thereby di
ffering from anionic or neutral porphyrins which can photosensitize th
e G- bacteria only after permeabilization of their outer membrane. The
present data show that the differences between these positively and n
egatively charged porphyrins are not related by a difference in the in
trinsic photosensitizing efficiency, as determined by the photo-oxidat
ion of model substrates or the yield of O-1(2) generation; moreover, t
here are only minor differences in the quantum yield of porphyrin phot
obleaching. Rather, it appears that the positive charge promotes an el
ectrostatic binding of the porphyrin to the outer cell surface inducin
g an initial limited damage which favours the penetration of the photo
sensitizer. Actually, the overall photoprocess is inhibited by the pre
incorporation of the porphyrin into liposomes, while it is enhanced by
using amphiphilic dicationic porphyrins which bind to endocellular si
tes in larger amounts and in a more stable form.