Nitrogenase from Rhodospirillum rubrum. Relation between 'switch-off' effect and the membrane component. Hydrogen production and acetylene reduction with different nitrogenase component ratios.

Nitrogenase activity of 'membrane-free' extracts, produced from nitrogen-starved Rhodospirillum rubrum to which 4 mM NH4+ had been added is only about 10% of the activity in the control. The activity could be restored to 80% by including the membrane component, earlier found to activate R. rubrum nitrogenase, in the reaction mixture. The relation between this 'switch-off/switch-on' effect and the function of the membrane component is discussed. Hydrogen production catalyzed by R. rubrum nitrogenase is also dependent on activation by the membrane component. Hydrogen production is inhibited by acetylene but the degree of inhibition is dependent on the nitrogenase component ratio. The strongest inhibition is achieved at low MoFe protein/Fe protein rations. The ATP/2E- values are 4-5 at the component ratios giving the highest activity and increase at high MoFe protein/Fe protein ratios. CO inhibits acetylene reduction but has no effect on the hydrogen production.