Gazarian I G, Lagrimini L M, George S J, Thorneley R N
Nitrogen Fixation Laboratory, John Innes Centre, Colney, Norwich, U.K.
Biochem J. 1996 Dec 1;320 ( Pt 2)(Pt 2):369-72. doi: 10.1042/bj3200369.
Tobacco peroxidase (36 kDa, pI 3.5) exhibits unique catalytic and spectral properties that are modulated by pH, calcium and magnesium ions. It catalyses the oxidation of veratryl alcohol by hydrogen peroxide over a wide pH range (1.5-5.0) in the presence of these metal ions with a pH optimum of 1.8. This is the only example of a holoperoxidase described so far that is active and comparatively stable at such a low pH. The enhancement of tobacco peroxidase activity by magnesium ions is to our knowledge the first example of a magnesium-induced peroxidase activation. UV/visible spectra of tobacco peroxidase showed that the Soret band shifted and its absorption coefficient increased upon the addition of calcium or magnesium ions and on lowering the pH. The tobacco peroxidase spectrum at pH 1.85, in the presence of calcium chloride (> 50 mM), is similar to that of lignin peroxidase at pH 6.0, with the Soret band shifting from 403 to 409 nm and the molar absorption coefficient increasing from 108,000 to 148,000 +/- 2000 M-1.cm-1 (results given +/- S.E.M.; n = 3). The data provide evidence for a low-affinity site for bivalent metal ion binding in addition to the two constitutive calcium sites that are present in all plant peroxidases. The presence of a glutamic acid residue (Glu-141) at the entrance to the haem-binding pocket, analogous to Glu-146 in lignin peroxidase and not present in other plant peroxidases, may account for these novel properties.
烟草过氧化物酶（36 kDa，pI 3.5）具有独特的催化和光谱特性，这些特性会受到pH值、钙离子和镁离子的调节。在这些金属离子存在的情况下，它能在较宽的pH范围（1.5 - 5.0）内催化过氧化氢氧化藜芦醇，最适pH为1.8。这是迄今为止所描述的全过氧化物酶中唯一一个在如此低的pH值下仍具有活性且相对稳定的例子。据我们所知，镁离子对烟草过氧化物酶活性的增强是镁诱导过氧化物酶激活的首个例子。烟草过氧化物酶的紫外/可见光谱表明，加入钙离子或镁离子以及降低pH值时，Soret带会发生移动且其吸收系数会增加。在氯化钙（> 50 mM）存在的情况下，pH 1.85时的烟草过氧化物酶光谱与pH 6.0时的木质素过氧化物酶光谱相似，Soret带从403 nm移至409 nm，摩尔吸收系数从108,000增加到148,000 +/- 2000 M-1.cm-1（结果给出 +/- 标准误；n = 3）。这些数据证明，除了所有植物过氧化物酶中都存在的两个组成性钙位点外，还存在一个二价金属离子结合的低亲和力位点。血红素结合口袋入口处存在一个谷氨酸残基（Glu - 141），类似于木质素过氧化物酶中的Glu - 146，而其他植物过氧化物酶中不存在，这可能解释了这些新特性。
