The role of NAD+ as a signal during nitrogenase switch-off in Rhodospirillum rubrum.
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'.
Norén
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A
Department of Biochemistry, Arrhenius Laboratories for Natural Sciences, Stockholm University, S-106 91 Stockholm, Sweden.
Soliman
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A
Nordlund
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S
D017037:Dinitrogenase Reductase / Q000378:metabolism; D009243:NAD / Q000378:metabolism / Q000494:pharmacology*; D009591:Nitrogenase / Q000378:metabolism*; D010084:Oxidation-Reduction; D012247:Rhodospirillum rubrum / Q000378:metabolism*
D017037:Dinitrogenase Reductase; D009243:NAD; D009591:Nitrogenase