Necessity of a membrane component for nitrogenase activity in Rhodospirillum rubrum

Acetylene reduction catalyzed by nitrogenase from Rhodospirillum rubrum has low activity and exhibits a lag phase. The activity can be increased by the addition of a chromatophore membrane component and the lag eliminated by preincubation with this component, which can be solubilized from chromatophores by treatment with NaCl. It is both trypsin- and oxygen-sensitive. Titration of the membrane component with nitrogenase and vice versa shows a saturation point. The membrane component interacts specifically with the Fe protein of nitrogenase, the interaction being ATP- and Mg2+-dependent.