固氮螺菌(Azospirillum.brasilenseYu-62)中固氮酶活性的氨关闭现象

NH_4^+ SWITCH-OFF OF NITROGENASE ACTIVITY IN AZOSPIRILLUM. BRASILENSE Yu-62

固氮螺菌(A.brasilense)Yu-62在以谷氨酸为氮源好气液体培养条件下,氨离子使固氮酶迅速失活,Western blotting实验证明这种失活的分子基础是固氮酶铁蛋白一亚基被修饰.测定加NH_4^+后细胞内α-ketoglutarte和glutamine的含量.α-ketoglutarate/glutamine比值在加NH_4^+后瞬间下降然后上升,而细胞内ATP/ADP的比值没有明显变化.谷氨酸合成酶的抑制剂azaserine使固氮酶失活.Western blotting实验表明这种失活的分子基础也是固氮酶铁蛋白一亚基被修饰.测定加azaserine后细胞内α-ketoglutarate及glutamine比值的变化以及外源α-ketoglutarate及glutamine对细胞固氮活性的影响,表明细胞内一些小分子化合物的变化可能是作用于固氮酶活性氨关闭的重要因素.

NH4+ switch-off of nitrogenase activity in A. brasilense Yu-62 cultured aerobically in liquid medium with glutamate as N source was described. Western blotting experiment demonstrated that the molecular basis of inactivation of nitrogenase was the modification of the Fe protein subunit. α-ketoglutarate and glutamine contents in cells were measured, after adding NH4+ , α-ketoglutarate/glutamine ratio reduced immediately then rised, but the ratio of ATP/ADP was no change. Azaserine (a inhibitor of GOGAT) inactivated nitrogenase activity rapidly, western blotting experiment demonstrated that the molecular basis of inactivation of nitrogenase was also the modification of the Fe protein subunit. To analyse the effects of azaserine on α-ketoglutarate/glutamine ratio and the effects of α-ketoglutarate and glutamine on the activity of nitrogenase in whole cells showed that the change of some small molecular in cells could be important factors in regulating NH4+ switch-off of nitrogenase activity.