Porphyrin-induced photodamage at the cellular and the subcellular level as related to the solubility of the porphyrin.

Porphyrin-induced photodamage has been studied on small organic molecules, biomolecules, mitochondria and red cells. Water soluble components (e.g. tryptophan and glutamate dehydrogenase) are more easily destroyed by uroporphyrin than by protoporphyrin. On the other hand, lipophilic components (e.g. succinate dehydrogenase, mitochondria and red cell membranes) are more severely damaged by protoporphyrin. The results may be of importance to explain the different skin lesions in erythropoietic protoporphyria and in porphyria cutanea tarda. The photodamage is enhanced by D2O and reduced by azide. Reagents known to increase or decrease the yields of superoxide, peroxide or hydroxyl radicals have no effect on the photodamage. The results suggest that singlet oxygen is the most important reactive oxygen species.