[邻二酚氧化酶的稳定性及催化特性。1. 邻二酚的氧化]

[Stability and catalytic properties of o-diphenol oxidase. 1. Oxidation of o-diphenols].

作者信息

Butovich I A

出版信息

Ukr Biokhim Zh (1978). 1986 Jan-Feb;58(1):10-6.

Abstract

o-Diphenoloxidase from potato tubers is inactivated in the course of the oxidation reaction of o-diphenols at the level of the enzyme-substrate complex. At 25 degrees C of the reaction mixture the enzyme inactivation rate constants (Kin) in oxidation of 10 mM solutions of the substrates were: for pyrocatechol--0.48 min-1; 3,4-dihydroxyphenylethylamine (DOP-amine)--0.52 min-1; 3,4-dihydroxyphenylalanine (DOPA)--0.17 min-1; noradrenaline--0.12 min-1; 3,4-dihydroxybenzaldehyde (DHBA)--0.032 min-1; 3,4-dihydroxybenzoic acid (DHBAc)--0.01 min-1; gallic acid--0.01 min-1. Kin of the enzyme in oxidation of pyrocatechol does not depend practically on pH, ionic strength and polarity of the medium, but rises with its temperature. For a temperature range from 20 to 40 degrees C the effective activation energy calculated in terms of the Arrhenius equation is equal to 28 kJ/mol and the preexponential value for the given preparation was 38 850 min-1. The enzyme activity is determined by the substituent nature in the substrate molecule: electron-donor groups (--CH2--) accelerate the oxidation as compared to nonsubstituted pyrocatechol and electron-acceptor groups (--COOH, --CHO) make it more difficult. If the o-diphenoloxidase activity in oxidation of a 10 mM solution of pyrocatechol is 100%, then the oxidation rate of DOP-amine taken in the same concentration would be 111, DOPA--61, noradrenaline--24, DOBA--2,7, DHBA--0.7, gallic acid--0.8%.(ABSTRACT TRUNCATED AT 250 WORDS)

摘要

马铃薯块茎中的邻二酚氧化酶在邻二酚的氧化反应过程中，于酶 - 底物复合物水平被灭活。在反应混合物温度为25℃时，底物10 mM溶液氧化过程中酶的失活速率常数（Kin）分别为：儿茶酚——0.48 min⁻¹；3,4 - 二羟基苯乙胺（DOP - 胺）——0.52 min⁻¹；3,4 - 二羟基苯丙氨酸（多巴）——0.17 min⁻¹；去甲肾上腺素——0.12 min⁻¹；3,4 - 二羟基苯甲醛（DHBA）——0.032 min⁻¹；3,4 - 二羟基苯甲酸（DHBAc）——0.01 min⁻¹；没食子酸——0.01 min⁻¹。儿茶酚氧化过程中该酶的Kin实际上不依赖于pH、离子强度和介质极性，但随温度升高而增加。在20至40℃温度范围内，根据阿伦尼乌斯方程计算的有效活化能等于28 kJ/mol，该制剂的指前因子值为38850 min⁻¹。酶活性取决于底物分子中的取代基性质：与未取代的儿茶酚相比，供电子基团（—CH₂—）加速氧化，而吸电子基团（—COOH、—CHO）则使其更难进行。如果10 mM儿茶酚溶液氧化时邻二酚氧化酶活性为100%，那么相同浓度的DOP - 胺氧化速率将为111%，多巴——61%，去甲肾上腺素——24%，DOBA——2.7%，DHBA——0.7%，没食子酸——0.8%。（摘要截选至250字）