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Uptake of Protoporphyrin and Violet Light Photodestruction of Propionibacterium acnes

Abstract The uptake of protoporphyrin IX by Propionibacterium acnes in suspension has been studied by fluorescence spectroscopy. Protoporphyrin, after it was injected into a cell suspension, was firstly bound to receptors on the cell surface and in this state protoporphyrin was non-fluorescent. Subsequently, probably as a result of lateral diffusion in the cell wall, these protoporphyrinreceptor complexes formed dimers. The final step in the overall uptake process of protoporphyrin by the cells from the surroundings consisted in a jum p of such dimers from waterlike to lipidlike com partm ents in the cell mem brane where protoporphyrin became fluorescent. The lipidlike com partm ents in the cells had a limited binding capacity of protoporphyrin. The fraction of surviving cells versus light dose has also been studied for varying amounts of protoporphyrin added to the cell suspensions. The survival curves were exponentially decaying with the irradiation time and there was a direct proportionality between the inverse slope of the survival curves and the intensity of protoporphyrin fluorescence from the lipidlike compartm ents. The relevance of these results to the therapy of Acne vulgaris is also discussed.