棕色固氮菌过氧化物酶研究

STUDIES ON THE PEROXIDASE FROM AZOTOBACTER VINELANDII-230

从具有固氮能力的棕色固氮菌（Azotobacter vinelandii）中首次分离纯化到一种高活性过氧化物酶。此酶分子量为150000道尔顿,由两个分子量相同的亚基组成。卟啉铁为其活性辅基。圆二色性谱表明酶分子中含有30%左右的α-螺旋。该酶最适 pH 6.0,最适温度37℃,在55℃迅速失去活性。此酶具有特殊的催化活性,在没有电子供体时,可催化单一底物——H2O2分解,即同时具有过氧化氢酶活性。以 H2O2为底物的动力学研究发现其具有别构酶特征,这在催化细胞内 H2O2分解时具有特殊的生理意义。用纯酶进行防氧保护酶与固氮酶组合实验,发现防氧酶系对防止 H2O2和 O2对固氮酶的损伤有显著保护作用。

The peroxidase from Azotobacter vinelandii-230 was purified.Its molecularweight is 155000 dalton.The result of SDS-gradient gel electrophoresis demo-nstrated that the peroxidase is constructed by two same subunits with moleoularweight 75000 dalton.The CD spectrum showed that the enzyme consists of 30%α-helix.The Visible-ultraviolet spectrum of it showed three intense absorption at405nm、556nm、630nm.This spectrum has the characteristics of porphyrins.Theiso electric point of it is pH 3.5.The optimum pH is 6.0.The optimum tempe-rature is 37℃.The enzyme has a special catalytic activity.When there is not any electron-donor,it can catalyze decomposition of H_2O_2、O_2.It has catalase activity.Studieson kinetics of catalytic reaction with only one substrate-H_2O_2 exhibited that theenzyme is a allosteric enzyme.We reconstructed the system of nitrogenase and O_2-protect enzymes and foundthat O_2-protect enzymes can prevent H_2O_2、O_2 from damage of nitrogenase O_2-pro-tect emzymes can protect activity of Nitrogenase in atmosphere or H_2O_2-solution.