A New Voltammetric Strategy for Investigating Reactive Iron-Sulfur Clusters

本研究的目的是定量研究蛋白质中铁-S簇的复杂反应活性。这些集群在自然界中执行着许多不同的功能。将使用一种新的方法，利用铁氧还蛋白(含有一个或两个簇的小蛋白)在氨基半胱醇存在下在石墨电极上显示的非介导性伏安法。铁氧还蛋白与氨基环醇共吸附，形成电活性薄膜。这使得非常经济、详细的研究成为可能，涉及含有与铁-S团簇反应的试剂的电解液之间的膜转移。通过EPR和MCD光谱分配给特定状态的伏安信号来控制簇氧化水平，并监测反应。克服了研究Fe-S团簇反应的一些长期存在的问题--还原电位很低，光谱特征差，不稳定和不稳定。阿姆斯特朗博士将描述(3Fe-4S)团簇的一种不同寻常的性质，即经历可逆、多电子和质子吸收的能力。这一性质代表了与目前认为蛋白质环境只允许非常保守的团簇氧化水平变化的观点的戏剧性背离。他将研究各种蛋白质中(3Fe-4S)对(M3Fe-4S)可逆金属离子吸收的平衡和动力学。将评估是否可能存在包含如锌等离子的团簇。他将比较不同(M3Fe-4S)团簇的氧化还原和配体结合特性。他将从铁和S的痕量水平研究蛋白质中簇组装的过程，并检查在竞争离子如锌存在的情况下这一过程的保真度。本研究探索这类重要化合物的特性，将有助于扩大我们对生命过程中氧化还原和电子转移的理解。

The aim of this study is to quantify complex reactivities of Fe-S clusters in proteins. These clusters perform numerous, diverse functions in nature. A novel methodology will be used, exploiting the unmediated voltammetry displayed by ferredoxins (small proteins containing one or two clusters) at graphite electrodes in the presence of aminocyclitols. Ferredoxins co-adsorb with aminocyclitols forming electroactive films. This makes possible highly economical, detailed studies involving film transfer between electrolytes containing reagents that react with Fe-S clusters. Cluster oxidation levels are controlled, and reactions are monitored via voltammetric signals assigned to specific states by EPR and MCD spectroscopy. Some longstanding problems of studying reactions of Fe-S clusters - very low reduction potentials, poor spectroscopic signatures, instability and lability - are overcome. Dr. Armstrong will characterize an unusual property of (3Fe-4S) clusters, the ability to undergo reversible, multiple electron and proton uptake. This property represents a dramatic departure from the current belief that the protein environment permits only very conservative changes in cluster oxidation level. He will examine the equilibria and kinetics of reversible metal ion uptake by (3 Fe-4S) to give (M3Fe-4S) in various proteins. The likely existence of clusters containing such ions as Zn will be assessed. He will compare the redox and ligand binding properties of various (M3Fe- 4S) clusters. He will study the course of cluster assembly in proteins, from trace levels of Fe and S, and examine the fidelity of this process in the presence of competing ions such as Zn. %%% This study, exploring the characteristics of this important class of compounds, will help to enlarge our understanding of oxidation -reduction and electron transfer in life processes.