Physicochemical and Structural Analysis fo Functions of Quinonoid Cofactors and Quinoproteins

1从氧化还原、酸碱反应和半醌自由基电子结构的角度阐明了细菌甲胺脱氢酶的辅因子色氨酸甲萘醌（TTQ）的理化性质和光谱性质。TTQ对氨的反应性，作为底物类似物，也进行了研究。这些物理化学和结构性质的意义已详细说明其在酶促反应中的功能。2柱电解光谱已被开发，以获得醌类和相关分子的光谱电化学性质。该方法已成功地应用于quinohemoprotein，乙醇脱氢酶的五步电子转移的热力学分析。3合成了几种模型化合物topa quinone，铜胺氧化酶的辅因子。采用TTQ和TPQ模型化合物以及吡咯并喹啉对醌催化胺氧化反应进行了详细的动力学分析 ...更多信息 喹啉醌（PQQ）。在催化反应过程中产生的反应中间体自由基的特征在于使用电子自旋共振光谱。所有这些结果都有力地支持了转氨作用机理。4醌类化合物的催化活性与电子结构之间的关系表明邻醌结构在催化胺氧化活性的表达中具有重要意义。邻位和对位醌型电子结构之间的自由TPQ模型化合物的互变异构化是负责其相对较低的催化活性，在胺氧化相比，TTQ和PQQ作为严格的邻醌。另一方面，已经发现半醌自由基参与还原醌的自氧化。5基于这些结果，Cu（II）的作用被认为是铜胺氧化酶中的瞬时分子内电子受体，以通过生成亚氨基-TPQ半醌来增强对分子氧的反应性，并且在含有TPQ的胺氧化酶中作为弱配体，以使TPQ辅因子携带邻位-醌型电子结构。少

1 Physicochemical and spectroscopic properties of tryptophan tryptophylquinone (TTQ), a cofactor bacterial methylamine dehydrogenase, have been elucidated in view of redox and acid-base reactions and semiquinone radical electronic structure. Reactivity of TTQ toward ammonia, as a substrate analog, has been also investigated. Significance of these physicochemical and structural properties have been detailed in relation with its function in the enzymatic reaction.2 Column-electrolytic spectroscopy has been developed in order to obtain spectroelectrochemical property of quinones and related molecules. This method has been successfully applied to the thermodynamic analysis of the five-step electron transfer of a quinohemoprotein, alcohol dehydrogenase.3 Several model compounds of topa quinone, a cofactor of copper amine oxidases, were synthesized. Detailed kinetic analysis has been performed concerning quinone-catalyzed amine oxidation using TTQ and TPQ model compounds as well as pyrroloqu … More inoline quinone (PQQ). A reaction intermediate radical generated during the catalytic reaction has been characterized using electron spin resonance spectroscopy. All these results strongly support a transamination mechanism.4 Relation between the catalytic activity and electronic structure of quinones suggests the significance of ortho-quinone structures in expression of the catalytic amine oxidation activity. Tautomerization of free TPQ model compounds between ortho-and para-quinone-type electronic structures is responsible for their relatively low catalytic activity in the amine oxidation compared with TTQ and PQQ as rigorous ortho-quinones. On the other hand, it has been found that semiquinone radicals participates is autoxidation of reduced quinones.5 On the basis of these results, roles of Cu (II) is proposed as a transient intramolecular electron acceptor in copper amine oxidases to enhance the reactivity toward dioxygen through the generation of the imino-TPQ semiquinone and as a weak ligand in TPQ-containing amine oxidases to make the TPQ cofactor to bear an ortho-quinone-type electronic structure. Less