Proton nuclear magnetic resonance study of histidine ionizations in myoglobins of various species. Comparison of observed and computed pK values.
Proton nuclear magnetic resonance study of histidine ionizations in myoglobins of various species. Comparison of observed and computed pK values.
复制标题
不同物种肌红蛋白中组氨酸电离的质子核磁共振研究。
DOI：
10.1021/bi00617a020
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发表时间：
1978
期刊：
影响因子：
2.9
通讯作者：
F. Gurd
中科院分区：
文献类型：
--
作者：
L. H. Botelho;S. Friend;J. B. Matthew;L. Lehman;G. Hanania;F. Gurd
Lynne H. Botelho, Stephen H. Friend, James B. Matthew，§Lee D. Lehman，§GI H. Hanania， 11和Frank R. N. Gurd*摘要：观察到的一系列肌红蛋白中组氨酸残基的pK值[Botelho， LH, and Gurd, FR N.(1978), Biochemistry 17（本期的前一篇论文）]与计算值进行了比较，这是基于Shire等人的修正，通过扩展了Tan-ford-Kirkwood理论[Shire， SJ, Hanania, GI H. and Gurd， F. r N.(1974) Biochemistry 13, 2967]。扩展处理利用抹香鲸肌红蛋白的三维结构来指定在给定的组氨酸残留物中哪个咪唑氮原子更容易暴露于溶剂。如果NT暴露程度越高，则选择pÁT′m为6.60，如果Nx暴露程度越高，则选择6.00，对应的分数静态溶剂为ac。本刊之前的论文报道了从16种动物中获得的一组肌红蛋白中观察到的组氨酸C-2质子共振的分配（Botelho和Gurd， 1978）。在8、12、35、36、48、81,113,116,119、128和152个残基上鉴定出组氨酸的共振。本报告从化学位移范围和pK值的角度来解释每种情况下观察到的滴定行为。根据Shire等人（1974a, b）对Tanford-Kirkwood静电理论（Tanford and Kirkwood, 1957; Tanford and Roxby, 1972）的推广，将观测到的pK值与计算值进行比较。该方法利用抹香鲸肌红蛋白的三维结构（Takano, 1977）来帮助确定主要参与质子平衡的特定咪唑或Nx （Botelho, 1975）。利用给定组氨酸残基中质子解离位点的选择（Botelho, 1975; Matthew et al., 1978b），首先，指定一个特定的内在pK值pA) nt，它反映了nt和Nx之间质子结合行为的内在差异（Reynolds et al., 1973），其次，在给定情况下适用的分数静态溶剂可及性（Lee和Richards, 1971; Matthew et al., 1978a）。所研究的肌红蛋白的计算机pA“i/2”值对应于给定组半滴定阶段的pK值，与实验结果吻合较好。
Lynne H. Botelho, Stephen H. Friend, James B. Matthew, § Lee D. Lehman, § GI H. Hanania, 11 and Frank R. N. Gurd* abstract: Observed pK values for histidine residues in a series of myoglobins [Botelho, LH, and Gurd, FR N.(1978), Biochemistry 17 (preceding paper in this issue)] were compared with computed values by an extension of the Tan-ford-Kirkwood theory based on the modification by Shire et al.[Shire, SJ, Hanania, GI H. and Gurd, F. R. N.(1974) Biochemistry 13, 2967], The extended treatment draws on the three-dimensional structure of sperm whale myoglobin to specify which imidazole nitrogen atom is the more exposed to solvent in a given histidine residue. The choice of pÁT¡ m is then taken as 6.60 if NT is the more exposed or 6.00 if Nx is the more exposed, and the corresponding fractional static solvent ac-The preceding paper in this issue reported assignments of histidine C-2 proton resonances observed among a set of myoglobins obtained from 16 animal species (Botelho and Gurd, 1978). The histidine resonances were identified with residues 8, 12, 35, 36, 48, 81,113,116,119, 128, and 152. The present report deals with the interpretation of the observed titration behavior in each case in terms of chemical-shift ranges and pK values. The observed pK values are compared with computed values based on the extension by Shire et al.(1974a, b) of the Tanford-Kirkwood electrostatic theory (Tanford and Kirkwood, 1957; Tanford and Roxby, 1972). The treatment draws on the three-dimensional structure of sperm whale myoglobin (Takano, 1977) to help specify the particular imidazoleNT or Nx involved primarily in the proton equilibrium (Botelho, 1975). This choice of proton dissociation site in a given histidine residue is used (Botelho, 1975; Matthew et al., 1978b), in turn, to specify, first, a particular intrinsic pK value, pA) nt, that reflects the inherent differences in protonbinding behavior betweenNT and Nx (Reynolds et al., 1973) and, second, the fractional static solvent accessibilitythat applies in the given case (Lee and Richards, 1971; Matthew et al., 1978a). The computer pA" i/2 values, corresponding to the pK applying at the stage of half titration of a given group, show good agreement with experiment for all the myoglobins studied.