Haaker H, Laane C, Hellingwerf K, Houwer B, Konings W N, Veeger C
Eur J Biochem. 1982 Oct;127(3):639-45. doi: 10.1111/j.1432-1033.1982.tb06920.x.
The nitrogenase activity in whole cells of Rhodopseudomonas sphaeroides could be inhibited by lowering the electrical potential across the cytoplasmic membrane. The membrane potential was partly dissipated either by lowering the light intensity or by the addition of a lipophilic cation, tetraphenylphosphonium. Under these circumstances, it was shown that the intracellular ATP/ADP ratio was not affected and that the inhibition of the whole cell nitrogenase activity was not due to an inactivation of the nitrogenase enzyme. From these results it is concluded that electron transport to nitrogenase in Rps. sphaeroides is dependent on a high membrane potential. The nitrogenase enzyme in whole cells could be inactivated by lowering the membrane potential across the cytoplasmic membrane by incubating the cells in the dark or in the light in the presence of uncouplers. Nitrogenase could be reactivated in the light in the absence of uncouplers. Some possible mechanisms of action of NH+4 inhibition of whole cell nitrogenase activity could be excluded. Inhibition by NH4Cl of whole cell nitrogenase activity in Rps. sphaeroides could neither be explained by a rapid inactivation of the nitrogenase enzyme, nor by an effect on the intracellular ATP/ADP ratio or the membrane potential. NH+4 inhibits whole cell nitrogenase activity not directly but probably after being assimilated by glutamine synthetase. The role of glutamine, glutamate and 2-oxoglutarate on the regulation of electron transport to nitrogenase will be discussed.
降低球形红假单胞菌全细胞中的跨细胞质膜电势可抑制固氮酶活性。通过降低光照强度或添加亲脂性阳离子四苯基鏻，膜电势会部分耗散。在这些情况下，结果表明细胞内ATP/ADP比值未受影响，且全细胞固氮酶活性的抑制并非由于固氮酶失活。从这些结果可以得出结论，球形红假单胞菌中向固氮酶的电子传递依赖于高膜电势。通过在黑暗中或在存在解偶联剂的光照下培养细胞，降低跨细胞质膜的膜电势可使全细胞中的固氮酶失活。在不存在解偶联剂的光照下，固氮酶可重新激活。可以排除NH₄⁺抑制全细胞固氮酶活性的一些可能作用机制。球形红假单胞菌中NH₄Cl对全细胞固氮酶活性的抑制既不能用固氮酶的快速失活来解释，也不能用对细胞内ATP/ADP比值或膜电势的影响来解释。NH₄⁺不是直接抑制全细胞固氮酶活性，而是可能在被谷氨酰胺合成酶同化后起作用。将讨论谷氨酰胺、谷氨酸和2-氧代戊二酸在调节向固氮酶的电子传递中的作用。
