Tamilarasan R, McMillin D R
Department of Chemistry, Purdue University, West Lafayette, IN 47907-3699.
Biochem J. 1989 Oct 15;263(2):425-9. doi: 10.1042/bj2630425.
U.v.-visible-absorption and e.p.r. spectroscopy were used to study the type 2 and type 3 copper centres in the mercury derivative of laccase. After treatment with peroxide the mercury derivative of laccase exhibits a fully developed absorption band at 330 nm (delta epsilon = 2900 +/- 100 M-1.cm-1, which is characteristic of type 3 copper in the oxidized state. In addition, there is a weak ligand-field absorption at 740 nm (epsilon = 380 +/- 30 M-1.cm-1), which can be assigned to the type 3 pair. Because the e.p.r. spectrum of the type 2 copper is well resolved in the case of the mercury derivative of laccase, for the first time we have been able to observe spectroscopic evidence for a pH-dependent structural transition that has been invoked to explain the kinetics of enzyme reduction [Andréasson & Reinhammar (1979) Biochim. Biophys. Acta 568, 145-156]. According to the e.p.r. data the pKa lies in the range 6-7, and comparisons with a model compound show that the spectral changes can plausibly be interpreted in terms of the deprotonation of a water molecule in the co-ordination sphere of the type 2 copper.
利用紫外可见吸收光谱和电子顺磁共振光谱研究了漆酶汞衍生物中的2型和3型铜中心。用过氧化物处理后，漆酶汞衍生物在330 nm处呈现出一个完全发展的吸收带（Δε = 2900 ± 100 M⁻¹·cm⁻¹），这是氧化态3型铜的特征。此外，在740 nm处有一个弱的配体场吸收（ε = 380 ± 30 M⁻¹·cm⁻¹），可归属于3型铜对。由于在漆酶汞衍生物的情况下2型铜的电子顺磁共振谱得到了很好的解析，我们首次能够观察到与pH相关的结构转变的光谱证据，这种转变被用来解释酶还原的动力学[Andréasson & Reinhammar (1979) Biochim. Biophys. Acta 568, 145 - 156]。根据电子顺磁共振数据，pKa在6 - 7范围内，与模型化合物的比较表明，光谱变化可以合理地解释为2型铜配位球中水分子的去质子化。
