Porphyrin-induced photodamage as related to the subcellular localization of the porphyrins.

In liver cells photodamage following externally added protoporphyrin affects predominantly membrane associated components, whereas photodamage by uroporphyrin also affects water-soluble components. Following excess endogenous production of porphyrins, protoporphyrin concentrates in the mitochondria and exerts its photodamaging effect primarily on the mitochondrial system, whereas uroporphyrin concentrates in lysosomes with release and inactivation of lysosomal enzymes when irradiated. The results may be of importance to explain the different skin lesions in porphyria cutanea tarda and erythropoietic protoporphyria.