STUDIES ON THE MECHANISM OF BACTERIA PHOTOSENSITIZATION BY MESOSUBSTITUTED CATIONIC PORPHYRINS

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.