Beyer W F, Fridovich I
Biochemistry. 1987 Mar 10;26(5):1251-7. doi: 10.1021/bi00379a008.
The iron-containing superoxide dismutase from Escherichia coli is inactivated by H2O2 to a limit of approximately 90%. When corrected for the H2O2-resistant portion, this inactivation was first order with respect to residual activity and exhibited a pseudo-first-order rate constant of 0.066 min-1 at 25 degrees C in 0.24 mM H2O2 at pH 7.8. The superoxide dismutase activity remaining after treatment with H2O2 differed from the activity of the native enzyme with respect to heat stability, inhibition by azide, and inactivation by light in the presence of rose bengal and by N-bromosuccinimide. The native and the H2O2-modified enzymes were indistinguishable by electrophoresis on polyacrylamide gels. Inactivation of the enzyme by H2O2 was accompanied by loss of tryptophan and some loss of iron, but there was no detectable loss of histidine or of other amino acids. H2O2 treatment caused changes in the optical spectrum of the enzyme. Inactivation of the enzyme by H2O2 depends upon the iron at the active site. Thus, the apoenzyme and the manganese-substituted enzyme were unaffected by H2O2. We conclude that reaction of H2O2 with the iron at the active site generates a potent oxidant capable of attacking tryptophan residues. A mechanism is proposed.
来自大肠杆菌的含铁超氧化物歧化酶被过氧化氢失活至约90%的限度。校正抗过氧化氢部分后，这种失活相对于残余活性呈一级反应，在25℃、pH 7.8的0.24 mM过氧化氢中表现出0.066 min⁻¹的准一级速率常数。用过氧化氢处理后剩余的超氧化物歧化酶活性在热稳定性、叠氮化物抑制以及在孟加拉玫瑰红存在下的光失活和N-溴代琥珀酰亚胺失活方面与天然酶的活性不同。在聚丙烯酰胺凝胶上电泳时，天然酶和经过氧化氢修饰的酶无法区分。过氧化氢使该酶失活的同时伴随着色氨酸的损失和一些铁的损失，但未检测到组氨酸或其他氨基酸的损失。过氧化氢处理导致该酶的光谱发生变化。过氧化氢使该酶失活取决于活性位点的铁。因此，脱辅基酶和锰取代的酶不受过氧化氢影响。我们得出结论，过氧化氢与活性位点的铁反应产生一种能够攻击色氨酸残基的强氧化剂。提出了一种机制。
