MOSSBAUER STUDIES OF LOW-SPIN FERRIC PROTEINS

低自旋铁中铁位置的物理表征 血红素蛋白是非常重要的工作在一个 对这些结构与功能关系的理解 系统。拟议的研究将调查以下两个方面 蛋白质结构：i)铁的配位场是怎样的 对氨基酸序列的轻微变化和 蛋白质的结构，以及II)对温度的依赖关系 自旋-晶格弛豫以及它如何随自旋晶格弛豫的变化而变化 溶剂型。第一线的调查是由 人工合成大鼠肝细胞色素b5基因在E. Coli，在那里以极大的数量表达，高达 占细胞总蛋白的20%。可以在中进行特定修改 通过盒诱变产生的细胞色素。这些修改后的 蛋白质将通过EPR和穆斯堡尔谱学进行研究，以及 光谱将由S=1/2自旋哈密顿量来参数化， 然后可以将其用作配位场的基础 铁位置的表征。 穆斯堡尔谱的温度依赖性将有助于 作为对蛋白质振动的分维模型的进一步检验 模式。各种血红素和铁硫化物的EPR测定 蛋白质表明，这些分子中的声子态密度 系统与一个模型一致，在该模型中，蛋白质具有 分数维1.1-1.8。这些测量是在 对于低于12K的温度。穆斯堡尔谱学是一种理想的 方法将这些研究扩展到15K温度范围- 200K因为1)穆斯堡尔的积分强度 光谱不像EPR那样是温度的函数； 和，2)EPR测量表明， 这些温度应该在穆斯堡尔所达到的范围内 光谱是敏感的。我们建议首先研究肌红蛋白叠氮化物 以及溶剂对其分数维的影响， 这项工作稍后将扩展到辣根过氧化物酶 氰化物络合物、细胞色素b5和小血红素模型 化合物。

The physical characterization of the iron site in low-spin ferric heme proteins is very important in working toward an understanding of the structure-function relationships in these systems. The proposed research will investigate two aspects of the protein structure: i) how the ligand field of the iron is perturbed by slight changes in the amino acid sequence and structure of the protein, and ii) the temperature dependence of the spin-lattice relaxation and how it varies with changes in the solvent. The first line of investigation is made possible by the expression of a synthetic rat hepatic cytochrome b5 gene in E. coli, where it is expressed in extremely large quantities, up to 20% of total cell protein. Specific modifications can be made in the cytochrome by cartridge mutagenesis. These modified proteins will be studied by EPR and Mossbauer spectroscopy, and the spectra will be parametrized by a S=1/2 Spin Hamiltonian, which can then be used as the basis for a ligand field characterization of the iron site. The temperature dependence of the Mossbauer spectra will serve as a further test of the fractal model for protein vibrational modes. EPR measurements of various heme and iron-sulfur proteins indicate that the phonon density of states in these systems is consistent with a model in which the protein has a fractional dimension of 1.1-1.8. These measurements were made for temperatures below 12K. Mossbauer spectroscopy is an ideal method to extend these studies to the temperature range 15K- 200K because 1) the integrated intensity of the Mossbauer spectrum is not as strong a function of temperature as is EPR; and, 2) EPR measurements indicate that the fluctuation rates for these temperatures should be in the range to which Mossbauer spectra are sensitive. We propose to first study myoglobin azide and the effects of the solvent on its fractional dimension, with the work later to be extended to the Horseradish peroxidase cyanide complex, cytochrome b5, and small heme model compounds.