CATALASE INACTIVATION FOLLOWING PHOTOSENSITIZATION WITH TETRASULFONATED METALLOPHTHALOCYANINES

Catalase (CAT) in solution or incorporated in erythrocytes and K562 le ukemic cells is inactivated during photosensitization with tetrasulfon ated metallophthalocyanines (MePcS(4)). The effect of added scavengers and D2O showed that both singlet oxygen and free radical species are involved in this process. Evidence was found that direct interactions of ground or excited-stated photosensitizers with CAT are not responsi ble for CAT inactivation. Specific techniques to probe early damage to the CAT structure involved optical and EPR spectroscopy, HPLC and pol yacrylamide gel electrophoresis analyses. Different primary events of photosensitized protein damage included oxidation of cysteine residues as well as other amino acids, as demonstrated by the formation of car bon-centered free radicals and the loss of absorbance at lambda = 275 nm. In parallel, we detected degradation of the CAT heme groups, accom panied by release of Fe(II) ions in solution. These combined phenomena initiate cross-linkages between CAT subunits and subsequent degradati on of the protein with formation of irreversible aggregates in solutio n. Phthalocyanine-mediated photoinactivation of cell-bound CAT results in loss of protection against accumulating H2O2, providing an additio nal pathway of phototoxicity.