Changes in the NAD(P)H concentration caused by addition of nitrogenase ‘switch‐off’ effectors in Rhodospirillum rubrum G‐9, as measured by fluorescence

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Abstract
The effect of nitrogenase ‘switch‐off’ effectors on the concentration of NAD(P)H in Rhodospirillum rubrum G‐9 was investigated by fluorescence. A rapid decrease in fluorescence was observed when cells, either N2‐grown or nitrogen‐starved, were subjected to the effectors, but not when sodium chloride or Tris buffer was added. No effects on the fluorescence were observed in non‐nitrogen fixing cultures except when NAD+ was added. The results strongly indicate that the redox state of the pyridine nucleotide pool affects the control of the regulation of nitrogenase activity in R. rubrum.