Zhang K, Stern E A, Ellis F, Sanders-Loehr J, Shiemke A K
Department of Physics, University of Washington, Seattle 98195.
Biochemistry. 1988 Sep 20;27(19):7470-9. doi: 10.1021/bi00419a045.
Extensive X-ray absorption fine structure measurements and analysis have been made on azidomet- and methemerythrin and on the native forms of oxy- and deoxyhemerythrin. Due to the availability of models that have been synthesized to mimic the active site of hemerythrin, it was possible to make a thorough assessment of the various errors in the structural parameters determined by the analysis. It is found that the largest source of error is the lack of complete transferability of amplitude and phase between the standards and hemerythrin. This is of particular importance in distinguishing the contributions of the second-shell low-Z atoms and, thus, has a substantial influence on the determination of the iron-iron distance. The internal consistencies of the various checks and a new formulation of error analysis for the structural parameters give us confidence in the structure determined for the active site. The main result is that as O2 is released from oxyhemerythrin, the mu-oxo bridge between the two iron atoms in the active site with an Fe-O distance of 1.8 A converts to a mu-hydroxo bridge in deoxyhemerythrin, expanding the Fe-O distance to 2.0 A. The Fe-Fe distance expands proportionally from 3.24 A in oxyhemerythrin to 3.57 A in deoxyhemerythrin so as to keep the Fe-O-Fe bridging angle approximately constant. These conclusions provide experimental support for the structures of oxy- and deoxyhemerythrin proposed previously on the basis of spectroscopic and preliminary X-ray crystallographic data.
已对叠氮高铁肌红蛋白和高铁肌红蛋白以及氧合高铁肌红蛋白和脱氧高铁肌红蛋白的天然形式进行了广泛的X射线吸收精细结构测量和分析。由于已合成了模拟高铁肌红蛋白活性位点的模型，因此有可能对分析确定的结构参数中的各种误差进行全面评估。结果发现，最大的误差来源是标准物与高铁肌红蛋白之间幅度和相位缺乏完全的可转移性。这在区分第二配位层低Z原子的贡献方面尤为重要，因此对铁-铁距离的测定有重大影响。各种检验的内部一致性以及结构参数误差分析的新公式使我们对活性位点确定的结构有信心。主要结果是，当氧从氧合高铁肌红蛋白中释放时，活性位点中两个铁原子之间的μ-氧桥（Fe-O距离为1.8埃）在脱氧高铁肌红蛋白中转变为μ-氢氧桥，Fe-O距离扩大到2.0埃。铁-铁距离从氧合高铁肌红蛋白中的3.24埃成比例地扩大到脱氧高铁肌红蛋白中的3.57埃，以便使Fe-O-Fe桥连角大致保持恒定。这些结论为先前基于光谱和初步X射线晶体学数据提出的氧合高铁肌红蛋白和脱氧高铁肌红蛋白的结构提供了实验支持。
