Lu J, Bender C J, McCracken J, Peisach J, Severns J C, McMillin D R
Department of Molecular Pharmacology, Albert Einstein College of Medicine, Yeshiva University, Bronx, New York 10461.
Biochemistry. 1992 Jul 14;31(27):6265-72. doi: 10.1021/bi00142a014.
The nuclear modulation effect in pulsed EPR spectroscopy was used to study the type 2 copper binding site in the mercury derivative of laccase (MDL) in which the type 1 copper is substituted by Hg(II). By comparing the three-pulse electron spin-echo modulations and Fourier transform spectra of MDL and several model compounds, we conclude that the imidazole groups of two histidyl amino acid residues are equatorially coordinated to Cu(II) in the type 2 site. Computer simulations of these data suggest that the remote nonbonding nitrogens of the two imidazoles possess nuclear quadrupole parameters e2qQ = 1.47 MHz and eta = 0.83. A(iso) values of these two nitrogens are not identical, being 1.5 and 2.0 MHz. We have also used samples of the enzyme exchanged with D2O to examine the coordination of the water to the type 2 copper site. The deuterium modulation that is resolved by taking the ratio of the time domain ESEEM data from native and D2O-exchanged enzyme indicates that there is an equatorial water ligand, and further data show that this water is displaced by azide.
脉冲电子顺磁共振波谱中的核调制效应被用于研究漆酶汞衍生物（MDL）中的2型铜结合位点，其中1型铜被Hg(II)取代。通过比较MDL和几种模型化合物的三脉冲电子自旋回波调制和傅里叶变换光谱，我们得出结论：两个组氨酸氨基酸残基的咪唑基团在2型位点中与Cu(II)呈赤道配位。对这些数据的计算机模拟表明，两个咪唑的远程非键合氮具有核四极参数e2qQ = 1.47 MHz和eta = 0.83。这两个氮的A(iso)值不相同，分别为1.5和2.0 MHz。我们还使用了与D2O交换的酶样品来研究水与2型铜位点的配位。通过取天然酶和D2O交换酶的时域电子自旋回波包络调制（ESEEM）数据的比值解析出的氘调制表明存在一个赤道水配体，进一步的数据表明该水被叠氮化物取代。
