Stimulation of nitrogenase by acetylene: fresh synthesis or conformational change

Alternate exposure of the nitrogen-fixing blue-green alga Anabaena L-31 to acetylene in air and ambient atmosphere resulted in substantial enhancement in the rate of acetylene reduction activity. The stimulation occurred even when protein synthesis was inhibited in the dark or in the presence of rifampicin and chloramphenicol. Residual nitrogenase of ammonium chloride treated cultures also showed the stimulation effect. The results indicate that the stimulation is due to a substrate (acetylene) mediated alteration of the enzyme molecule and not due to fresh synthesis