Uptake of Protoporphyrin and Violet Light Photodestruction of Propionibacterium acnes

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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 cell wall, these protoporphyrin-receptor complexes formed dimers. The final step in the overall uptake process of protoporphyrin by the cells from the surroundings consisted in a jump of such dimers from waterlike to lipidlike compartments in the cell membrane where protoporphyrin became fluorescent. The lipidlike compartments 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 protoprophyrin fluorescence from the lipidlike compartments. The relevance of these results to the therapy of Acne vulgaris is also discussed.