Relationships between nitrogenase, glutamine synthetase, glutamine, and energy charge in Azotobacter vinelandii
Relationships between nitrogenase, glutamine synthetase, glutamine, and energy charge in Azotobacter vinelandii
复制标题
维氏固氮菌固氮酶、谷氨酰胺合成酶、谷氨酰胺与能量电荷之间的关系
作者：
J. Kleinschmidt;D. Kleiner
当棕色固氮菌连续培养物中加入完全抑制固氮酶合成的铵或硝酸盐时，细胞内谷氨酰胺水平和谷氨酰胺合成酶（GS）的腺苷酰化程度仅略有增加（分别从0.45-0.50 mM和从2 - 3），而总GS水平不受影响。较高的铵量另外抑制固氮酶的活性，引起细胞内谷氨酰胺浓度和GS的腺苷酸化的强烈上升，但没有引起ATP/ADP比率的变化。这些结果被认为是在A. vinelandii的研究表明，固氮酶合成的调节与GS的腺苷酸化状态和细胞内谷氨酰胺水平无关，并且由于高的细胞外铵水平而导致的固氮酶活性的抑制不是通过能荷的变化介导的。
When continuous cultures of Azotobacter vinelandii were supplied with ammonium or nitrate in amounts, which just repressed nitrogenase synthesis completely, both the intracellular glutamine level and the degree of adenylylation of the glutamine synthetase (GS) increased only slightly (from 0.45–0.50 mM and from 2 to 3 respectively), while the total GS level remained unaffected. Higher amounts of ammonium additionally inhibited the nitrogenase activity, caused a strong rise in the intracellular glutamine concentration and adenylylation of the GS, but caused no change in the ATP/ADP ratio. These results are considered as evidence that in A. vinelandii the regulation of nitrogenase synthesis is not linked to the adenylylation state of the GS and to the intracellular glutamine level, and that the inhibition of the nitrogenase activity as a consequence of a high extracellular ammonium level is not mediated via a change in the energy charge.