FREE RADICALS IN BIOLOGICAL REDOX PROCESSES

生物环境中的自由基通常会引发破坏性的 反应，由于它们的高反应性和非特异性化学。 然而，最近发现了两类新的酶 在正常的反应过程中，会产生哪些活性基团 催化作用。在第一节课中，自由基位是氨基。 酸性侧链；在第二种中，半喹酮类衍生于 精致的氨基酸侧链或来自外源辅因子提供 激进的中间派。这些顺磁性物种似乎是 这些酶的正常功能。了解通过哪些方式实现这些 自由基被生成、稳定并直接用于有效的催化 这是该项目的一个主要的长期目标。以一种方式 未配对的电子自旋密度分布在自由基中心为1 激进的反应性似乎受到控制的手段。当地人 蛋白质周围的氧化还原活性侧链是第二条 引导这些物种的反应性的重要因素，以及 它们在多大程度上被总蛋白质保护而不受溶剂的影响 结构是第三个。控制特征--将在 即将到来的赠款期限在各种部首的产生和利用中 酵素。我们打算重点关注的具体系统包括 放氧生物体中的光系统I和II； 核苷酸还原酶、前列腺素H合成酶、光解酶、 甲胺脱氢酶、甲醇脱氢酶和细胞色素Bc1。这个 这些酶产生的自由基包括酪氨酸、色氨酸、 半胱氨酸，以及从色氨酸色氨酸衍生的半喹酮， 吡咯喹啉醌和泛醌。在这些系统中的一些系统上工作 将只在密歇根州立大学完成；其他将被研究 通力合作。我们将应用的方法包括 微生物学、分子生物学、生物化学、光谱学和 计算化学。EPR、Endor和ESE光谱仪提供 主要的分析工具，旨在评估未配对的电子 自旋密度分布、自由基结构、局域环境 自由基位周围，以及溶剂的可及性。酪氨酸自由基是 迄今为止最具特点的，并将继续成为主要关注点 拟议中的工作。到目前为止，含有自由基的酶一直是 在某种程度上偶然发现的。通过详细描述这些物种的特征 在它们出现的那些酶中，我们预计一般 它们的催化活性原理将会出现，并导致它们 在其他酶反应中进行鉴定。

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.