Norén A, Soliman A, Nordlund S
Department of Biochemistry, Arrhenius Laboratories for Natural Sciences, Stockholm University, S-106 91 Stockholm, Sweden.
Biochem J. 1997 Mar 15;322 ( Pt 3)(Pt 3):829-32. doi: 10.1042/bj3220829.
The role of NAD+ in the metabolic regulation of nitrogenase, the 'switch-off' effect, in Rhodospirillum rubrum has been studied. We now show that the decrease in nitrogenase activity upon addition of NAD+ to R. rubrum is due to modification of dinitrogenase reductase. There was no effect when NAD+ was added to a mutant of R. rubrum devoid of dinitrogenase reductase ADP-ribosyltransferase, indicating that NAD+ 'switch-off' is an effect of the same regulatory system as ammonium 'switch-off'. We also show that oxaloacetate and alpha-ketoglutarate function as 'switch-off' effectors. On the other hand beta-hydroxybutyrate has the opposite effect by shortening the 'switch-off' period. Furthermore, by using an inhibitor of glutamate synthase the role of this enzyme in 'switch-off' was investigated. The results are discussed in relation to our proposal that changes in the concentration of NAD+ are involved in initiating 'switch-off'.
已经研究了NAD⁺在红螺菌中对固氮酶代谢调节的作用，即“关闭”效应。我们现在表明，向红螺菌中添加NAD⁺后固氮酶活性的降低是由于二氮酶还原酶的修饰。当将NAD⁺添加到缺乏二氮酶还原酶ADP-核糖基转移酶的红螺菌突变体中时没有效果，这表明NAD⁺的“关闭”与铵的“关闭”是同一调节系统的作用。我们还表明，草酰乙酸和α-酮戊二酸作为“关闭”效应物起作用。另一方面，β-羟基丁酸酯通过缩短“关闭”期具有相反的作用。此外，通过使用谷氨酸合酶抑制剂研究了该酶在“关闭”中的作用。结合我们提出的NAD⁺浓度变化参与启动“关闭”的建议对结果进行了讨论。
