番茄果实ACC合成酶的性质

Properties of Tomato Fruit ACC Synthase

测定了经4步纯化、比活性达20000U／mg蛋白质以上的番茄果实伤诱导ACC合成酶的一些酶学性质。酶反应最适PH值为9．5；酶在pH8．0下最稳定，pH7．5－10短时间处理不会使酶发生不可逆变性；酶在pH8．0和9．5的Km值分别为23和4Dμmol／L；根据酶反应不同时间的产物累积量，得出反应速度随时间的变化符合函数关系式Vt＝V0e－kt，并根据此式求出酶的半寿期为107min。光照对酶活性有抑制作用。酶的DTNB化学修饰结果表明，在酶活性中心的PLP结合部位很可能有半胱氨酸残基存在。

1 - Aminocycloopropane - 1 -car boxylate (ACC) synthase (EC 4, 4, 1,14) is the key enzyme regulating ethylene biosynthesis in higher plants. Someproperties of ACC synthase purified fromwound-induced tomato fruit were examined in this study. The enzyme's specific activity reached more than 20 000 Umg-1' protein by four-step purification.The optimum pH of the enzyme reactionwas 9. 5. ACC synthase activity was stablest at PH 8. 0 and no irreversible denaturation occurred when the enzyme waskept at pH 7.5 ~ 10 for 24 h. Km values of the enzyme at pH 8 .0 and pH 9. 5were 23 μmol/L and 40 μmol/L, respectively. The change of reaction ratewith time can be expressed with the equation Vt = V0e-kt, on the basis of accumulative product at different times of theenzyme reaction and the half -life periodwas found to be 107 minutes. Light hadinhibitory effect .on ACC synthase activity, which might result from sensitizedphotooxdation with pyridozal-5 '-phosphate as photosensitizer. The result ofchemical modification of ACC synthaseby DTNB indicates that cysteine residue(s) may be a component of PLP bindingposition at the active center of the enzyme.