酪氨酸酶 来源于菌菇

多酚氧化酶(酪氨酸酶)是一种双功能的含铜氧化酶，具有儿茶酚酶和解析酶活性。从系统发育的角度来看，它是褐变反应的原因。这种酶的分子量是128kda。它是一种四聚物，每个分子含有四个铜原子和包括酚类基质在内的芳香族化合物的两个结合位点。氧气有一个独特的结合位点。最佳 ph 值范围是6-7。在25 ° c，ph 值6.5时，一个单位能使280 nm 处的吸收度增加0.001/min，以 l- 酪氨酸为下位药物。抑制剂: 与铜络合的化合物。苯甲酸对邻苯二酚竞争性地抑制该酶，氰化物对氧竞争性地抑制该酶。 产品介绍： 多酚氧化酶(酪氨酸酶)是一种双功能的含铜氧化酶，具有儿茶酚酶和解析酶活性。从系统发育的角度来看，它是褐变反应的原因。这种酶的分子量是128kda。它是一种四聚物，每个分子含有四个铜原子和包括酚类基质在内的芳香族化合物的两个结合位点。氧气有一个独特的结合位点。最佳 ph 值范围是6-7。酶活定义：使用L-酪氨酸作为底物，在25°C、pH 6.5的条件下，一个单位导致280 nm处的吸光度每分钟增加0.001。 Inhibitors Compounds that complex with copper. The enzyme is also inhibited competitively by benzoic acid with respect to catechol and by cyanide with respect to oxygen (Duckworth and Coleman 1970). Stability The lyophilized preparation is stable for 6-12 months when stored at -20°C. Activity Polyphenol oxidase is an oxygen transferring enzyme. Besides using O2 to catalyze the dehydrogenation of catechols to orthoquinones and the orthohydroxylation of phenols to catechols, a peroxidase activity has been reported on by Strothkamp and Mason (1974). Kinetic studies have been reported by Kertész et al. (1971). See also the review by Malmström and Rydén. Polyphenol Oxidase Assay Method Polyphenol oxidase oxidizes tyrosine to dihydroxyphenylalanine which in turn is oxidized to o-quinone. The latter is accompanied by an increase in absorbance at 280 nm. The rate of increase is proportional to enzyme concentration and linear during a period of 5-10 minutes after an initial lag. One unit causes a change in absorbance at 280 nm of 0.001 per minute at 25°C, pH 6.5 under the specified conditions. Reagents 0.5 M Potassium phosphate buffer, pH 6.5 0.001 M L-Tyrosine Enzyme Dissolve at a concentration of 1 mg/ml in reagent grade water. Dilute further in reagent grade water to a concentration of 200-400 units/ml. Procedure Adjust the spectrophotometer to 280 nm and 25°C. Pipette into each cuvette as follows: 0.5 M Phosphate buffer, pH 6.5 1.0 ml 0.001 M L-Tyrosine 1.0 ml Reagent grade water 0.9 ml Oxygenate this reaction mixture by bubbling oxygen into cuvettes through a capillary tube for 4-5 minutes. Transfer cuvettes to the spectrophotometer and record A280 for 4-5 minutes to achieve temperature equilibration and to establish blank rate, if any. Add 0.1 ml of appropriately diluted enzyme and record A280 for 10-12 minutes. Determine ΔA280 from the linear portion of the curve. A non-linear "lag" of 2-3 minutes can be expected. Calculation

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