Ugarova N N, Rozhkova G D, Berezin I V
Biochim Biophys Acta. 1979 Sep 12;570(1):31-42. doi: 10.1016/0005-2744(79)90198-0.
Chemical modification of horseradish peroxidase (donor:hydrogen-peroxide oxidoreductase, EC 1.11.1.7) (isoenzyme C) by anhydrides of mono- and dicarboxylic acids and picryl sulfonic acid has been performed. The effect of the modification on the catalytic activity, absorption and circular dichroism spectra of peroxidase has been studied. Rate constants of irreversible thermoinactivation (kin) for the native and modified peroxidase at 56--80 degrees C have been measured. The effective values of the thermodynamic activation parameters of thermoinactivation, delta H not equal to and delta S not equal to, have been also determined. A relationship between the number of modified epsilon-amino groups of lysine residues and the nature of the modifier on the one hand, and the conformation and thermostability of the enzyme on the other, is discussed. It has been shown that it is the degree of modification, rather than the nature of the modifier, that produces the major effect on the macromolecular conformation and the thermostability of the enzyme after modification. The conclusion is drawn that the thermostability of the modified enzyme increases due to the decrease of the conformational mobility in the protein moiety around the heme.
已用一元羧酸和二元羧酸的酸酐以及苦味酸磺酸对辣根过氧化物酶（供体：过氧化氢氧化还原酶，EC 1.11.1.7）（同工酶C）进行了化学修饰。研究了修饰对过氧化物酶催化活性、吸收光谱和圆二色光谱的影响。测定了天然和修饰过氧化物酶在56 - 80℃下不可逆热失活的速率常数（kin）。还确定了热失活的热力学活化参数的有效值，即ΔH≠和ΔS≠。讨论了一方面赖氨酸残基的修饰ε-氨基数量与修饰剂性质之间的关系，另一方面与酶的构象和热稳定性之间的关系。结果表明，对修饰后酶的大分子构象和热稳定性产生主要影响的是修饰程度，而非修饰剂的性质。得出的结论是，修饰酶的热稳定性增加是由于血红素周围蛋白质部分构象流动性的降低。
