Protoporphyrin photosensitization of Enterococcus hirae and Candida albicans cells

Protoporphyrin IX (PP) (1 or 10 g ml-1) was added to aqueous suspensions of Entorococcus hirae, a Gram-positive bacterium, and Candida albicans, a yeast. Washing of the incubated cells with phosphate-buffered saline (PBS) showed that the percentage of tightly bound PP was 26.8-4% or 1.6-1.5%, respectively. Upon visible light-illumination, both species display a similar degree of photosensitivity. Electrophoretic analyses indicate that cytoplasmic membrane proteins are the primary target of PP photosensitization, while DNA damage is detectable only at relatively long irradiataion times, especially for E. hirae. Autoradiographic analyses of thin sections pointed out that PP is released from cells during irradiation; the processi s more evident for E. hirae. These indications suggests a partially different mechanism of cell photodamage in the two species, similar to that previously observed using haematophorphyrin as a sensitizer.