FREE RADICALS IN BIOLOGICAL REDOX PROCESSES

生物环境中的自由基通常会引起破坏性的 反应，由于其高反应性和非特异性化学。 然而，最近，两类新的酶已被确定， 其中反应性自由基物质是在正常过程中产生的 催化作用在第一类中，自由基位点是氨基， 酸侧链;在第二，半醌衍生自 精细的氨基酸侧链或来自外源辅因子提供了 激进中心这些顺磁性物质似乎是不可或缺的， 这些酶的正常功能。了解这些 自由基的产生，稳定，并直接有效的催化， 这是该项目的长期目标。的方式 不成对电子自旋密度分布在径向中心为1 自由基反应性似乎受到控制的手段。当地 氧化还原活性侧链周围的蛋白质环境是第二个 在引导这些物种的反应性的重要因素，和 它们被整体蛋白质屏蔽溶剂的程度 结构是第三种。控制功能-将在研究 即将到来的赠款期间，在各种自由基产生和利用 内切酶我们打算重点关注的具体系统包括 光系统I和II在放氧生物体中; 核糖核苷酸还原酶，前列腺素H合酶，光裂合酶， 甲胺脱氢酶、甲醇脱氢酶和细胞色素BC 1。的 由这些酶产生的自由基包括酪氨酸，色氨酸， 半胱氨酸，和衍生自色氨酸的半醌， 吡咯并喹啉醌和泛醌。在其中一些系统上工作 将专门在密歇根州进行;其他人将被研究 合作。我们将应用的方法包括以下技术： 微生物学、分子生物学、生物化学、光谱学， 计算化学EPR、ENDOR和ESE光谱提供了 主要分析工具，旨在评估未配对电子 自旋密度分布，自由基结构，局域环境 以及溶剂的可及性。酪氨酸自由基是 迄今为止最好的特点，并将继续成为主要焦点 的拟议工作。到目前为止，含自由基的酶已经被 偶然发现的。通过详细描述这些物种 在这些酶中，我们预计， 其催化活性的原理将出现，并导致其 在其他酶促反应中鉴定。

Free radicals in biological milieu generally provoke destructive reactions, owing to their high reactivity and non-specific chemistry. Recently, however, two new classes of enzymes have been identified in which reactive radical species are generated during the normal course of catalysis. In the first of these classes, the radical site is an amino acid side chain; in the second, semiquinones derived either from elaborated amino acid side chains or from exogenous cofactors provide the radical center. These paramagnetic species appear to be integral to the proper function of these enzymes. Understanding the means by which these radicals are generated, stabilized, and directed to effective catalysis is a major, long-term objective of the project. The manner in which the unpaired electron-spin density is distributed on the radical center is one means by which radical reactivity appears to be controlled. The local protein environment around the redox active side chain is a second important factor in channeling the reactivity of theses species, and the extent to which they are shielded from solvent by the overall protein structure is a third. The controlling features-will be studied in the upcoming grant period in a variety of radical-generating and utilizing enzymes. The specific systems upon which we intend to focus include the following: Photosystems I and II in oxygen-evolving organisms; ribonucleotide reductase, prostaglandin H synthase, photolyase, methylamine dehydrogenase, methanol dehydrogenase and cytochrome bc1. The radicals generated by these enzymes include tyrosine, tryptophan, cysteine, and the semiquinones derived from tryptophan tryptophylquinone, pyrroloquinoline quinone, and ubiquinone. Work on some of these systems will be done exclusively at Michigan State; others will be studied collaboratively. The methods we will apply include techniques from microbiology, molecular biology, biochemistry, spectroscopy, and computational chemistry. EPR, ENDOR, and ESE spectroscopies provide the primary analytical tools and are intended to assess the unpaired electron spin-density distribution, the radical structure, the local environment around the radical site, and solvent accessibility. Tyrosine radicals are the best characterized thus far and will continue to be the primary focus of the proposed work. Thus far, radical-containing enzymes have been uncovered somewhat accidentally. By characterizing these species in detail in those enzymes in which they occur, we anticipate that general principles of their catalytic activity will emerge and lead to their identification in other enzymatic reactions.