漆树漆酶的催化氧化作用──Ⅵ．漆酶的催化氧化反应机理研究

漆树漆酶的催化氧化作用──Ⅵ．漆酶的催化氧化反应机理研究 CATALYZED OXIDATION BY RHUS VERNICIFERA LACCASE Ⅵ. STUDIES ON MECHANISM OF ENZYMATIC OXIDATION REACTION BY RHUS LACCASE 王光辉 1 first-author 江涛 1 武汉大学化学系 武汉大学化学系 Department of Chemistry, Wuhan University Department of Chemistry, Wuhan University 在静止条件下，用分光光度法研究了底物２，３－二氰基－５，６－二卤氢醌（ＤＤＸＱＨ２，Ｘ＝Ｃｌ，Ｂｒ．Ｉ）的漆酶催化氧化反应，考察了底物离解与反应的关系，考察了半醌自由基的形成和衰减动力学，测定了不同ｐＨ条件下的表现反应速度常数（ｋｏｂｓｄ）、米氏常数（ｋｍ）、半醌自由基的形成速度常数（ｋｆ）和半醌自由基的衰减速度常数（ｋ２ｄ），探讨了环境对半醌自由基形成与衰减的影响，鉴定了反应最终产物的结构．结果证明：１）、底物的一级离解种是底物参与反应的必要形式；２）、半醌自由基阴离子是酶反应的直接产物；３）、半醌自由基的衰减是非酶的歧化反应，４）、由酶反应和非酶反应两部分构成的反应全过程是通过半醌自由基的形成和衰减作纽带联系着的，两个反应部分既独立又偶联，表现为一种特殊的连串反应属性．在此基础上，提出了邻、对苯二酚的漆酶催化氧化反应机理． in static condition, the Rhus laccase-catalyzed oxidation reaction of 2, 3-dicyano-5,6-dihalohydroquinone （DDXQH2, X=Cl, Br or I） was studied by spectrophotometry. The relationship of dissociation and reation of substrates was investisated. The various kinetic parameters, including the observed first order rate constantS （kobsd） and Michaelis constants （k.） of the enzymatic oxidation of subStrates, the formation rate constants of semiquinone radicals （k,） and the second order disproportionation rate constants of semiquineone radicals （k2d）, were determined. The influance of PH on the formation and decay of semiquinone radicals was ascertained. The end products of enzymatic oxidation of substrates were identified. These results were demonstrated that: （1）, the monoanion formof subStrates is active species and participant of enzymatic reaction; （2）, the semiquinone anion--radical is direct product of enzymatic reaction i （3）, the decay of semiquinone anion--radical is non￣enzymatic diSProportionation reaction; （4）, the, whole process involve two section of the enzymatiC reaction and the non-enzymatic reaction, furthermore the relationship between the two section iS not onlyindependent but coupling, and they maintain close ties with formation and decay of semiquinone anion-radical; for this reason, this process appears obviously a characteristics of consedutive reaction.On the basis of these results, a mechanism of Rhus laccase-catalyzed oaldation reaction of o-,p-diphenols was proposed and discussed. 漆树漆酶 2 3－二氰基－5 6－二卤氢醌 酶催氧化 反应机理 分光光度法 Q554.9 国家自然科学基金(61672102) 1994-01-01 2021-04-01 1