Gantchev T G, van Lier J E
Department of Nuclear Medicine and Radiobiology, Faculty of Medicine, University of Sherbrooke, Quebec, Canada.
Photochem Photobiol. 1995 Jul;62(1):123-34. doi: 10.1111/j.1751-1097.1995.tb05248.x.
Catalase (CAT) in solution or incorporated in erythrocytes and K562 leukemic cells is inactivated during photosensitization with tetrasulfonated metallophthalocyanines (MePcS4). 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 photosensitizer with CAT are not responsible for CAT inactivation. Specific techniques to probe early damage to the CAT structure involved optical and EPR spectroscopy, HPLC and polyacrylamide 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 carbon-centered free radicals and the loss of absorbance at lambda = 275 nm. In parallel, we detected degradation of the CAT heme groups, accompanied by release of Fe(II) ions in solution. These combined phenomena initiate cross-linkages between CAT subunits and subsequent degradation of the protein with formation of irreversible aggregates in solution. Phthalocyanine-mediated photoinactivation of cell-bound CAT results in loss of protection against accumulating H2O2, providing an additional pathway of phototoxicity.
溶液中或掺入红细胞及K562白血病细胞中的过氧化氢酶（CAT）在用四磺酸化金属酞菁（MePcS4）进行光致敏过程中会失活。添加清除剂和重水的作用表明，单线态氧和自由基均参与了此过程。有证据表明，基态或激发态光敏剂与CAT的直接相互作用并非CAT失活的原因。用于探测CAT结构早期损伤的特定技术包括光学和电子顺磁共振光谱、高效液相色谱以及聚丙烯酰胺凝胶电泳分析。光敏蛋白损伤的不同初级事件包括半胱氨酸残基以及其他氨基酸的氧化，以碳中心自由基的形成以及在λ = 275 nm处吸光度的损失为证。同时，我们检测到CAT血红素基团的降解，伴随着溶液中Fe(II)离子的释放。这些综合现象引发CAT亚基之间的交联以及随后蛋白质的降解，并在溶液中形成不可逆聚集体。酞菁介导的细胞结合型CAT的光失活导致对积累的H2O2的保护作用丧失，提供了一条额外的光毒性途径。
