棕色固氮菌固氮酶钼铁蛋白两种聚合体的研究

 棕色固氮菌固氮酶钼铁蛋白八聚体相当于两个钼铁蛋白四聚体的聚合体。在细胞生长过程中,胞内钼铁蛋白两种聚合体的相对含量出现规律性变化:在对数期,细胞固氮酶比活力成上升趋势,而钼铁蛋白主要以高活力的四聚体形式存在;在对数期结束至稳定期,细胞固氮酶比活力下降至一个低水平的稳定值,此时的钼铁蛋白基本上为八聚体形态。在细胞固氮生长时,向培养基中加入过量氨可明显地导致钼铁蛋白由四聚体向八聚体的转化。我们推断,生长过程中胞内钼铁蛋白聚合态的变化可能是调节固氮酶活力的一种方式。胞外,钼铁蛋白的两种聚合态可以相互转化。

Studies on the Octameric and Tetrameric Molybdenum-iron Proteins of Nitrogenase From Azotobacter Vinelandii

We have found and purified the octamer of molybdenum-iron protein of nitrogenase from Azotobacter vinelandii 230. The activity of the octamer is lower than that of the tetramer. The octamer formation in vivo is related to cell growth process. During the log-phase of cell growth, the specific activity of nitrogenase is increasing, and the tetramer is the major form of molybdenum-iron protein. After entering into the plateau-phase, the energy activity decreases from maximum quickly and tends to stabilize at a low value, and at the same time the octamer becomes the major form of molybdenum-iron protein. Adding ammonium to the culture medium during nitrogen-fixing growth stage of Azotobacter vinelandii induces the formation of the octamer obviously. We suggest that, the octamer of molybdenum-iron protein is a possible metablite in regulation of nitrogenase activity, the conversion from the tetramer to octamer will cause the decrease of nitrogenase specific activity in vivo. The octamer converts to tetramer at 4℃ in vitro, and the direction of conversion is reversed at 30℃.