Gebicka L, Gebicki J L
Institute of Applied Radiation Chemistry, Technical University of Lódź.
Acta Biochim Pol. 1996;43(4):673-8.
The reactions of two heme peroxidases, horseradish peroxidase and lactoperoxidase and their compounds II (oxoferryl heme intermediates, Fe(IV) = O or ferric protein radical Fe(III)R.) and compounds III (resonance hybrids [Fe(III)-O2-.<--> Fe(II)-O2] with superoxide radical anion generated enzymatically or radiolytically, and with hydroxyl radicals generated radiolytically, were investigated. It is suggested that only the protein radical form of compound II of lactoperoxidase reacts with superoxide, whereas compound II of horseradish peroxidase, which exists only in oxoferryl form, is unreactive towards superoxide. Compound III of the investigated peroxidases does not react with superoxide. The lactoperoxidase activity loss induced by hydroxyl radicals is closely related to the loss of the ability to form compound I (oxoferryl porphyrin pi-cation radical, Fe(IV) = O(Por+.) or oxoferryl protein radical Fe(IV) = O(R.)). On the other hand, the modification of horseradish peroxidase induced by hydroxyl radicals has been reported to cause also restrictions in substrate binding (Gebicka, L. & Gebicki, J.L., 1996, Biochimie 78, 62-65). Nevertheless, it has been found that only a small fraction of hydroxyl radicals generated homogeneously does inactivate the enzymes.
研究了两种血红素过氧化物酶，即辣根过氧化物酶和乳过氧化物酶及其化合物II（氧合铁血红素中间体，Fe(IV)=O或铁蛋白自由基Fe(III)R.）和化合物III（共振杂化物[Fe(III)-O2-<-->Fe(II)-O2]，通过酶促或辐射产生超氧阴离子自由基，以及通过辐射产生羟基自由基）的反应。结果表明，只有乳过氧化物酶化合物II的蛋白自由基形式与超氧反应，而仅以氧合铁形式存在的辣根过氧化物酶化合物II对超氧无反应。所研究的过氧化物酶的化合物III不与超氧反应。羟基自由基诱导的乳过氧化物酶活性丧失与形成化合物I（氧合铁卟啉π-阳离子自由基，Fe(IV)=O(Por+.)或氧合铁蛋白自由基Fe(IV)=O(R.)）的能力丧失密切相关。另一方面，据报道，羟基自由基诱导的辣根过氧化物酶修饰也会导致底物结合受限（Gebicka, L. & Gebicki, J.L., 1996, Biochimie 78, 62-65）。然而，已经发现，均匀产生的羟基自由基中只有一小部分会使酶失活。
