Physiological electron donor systems to the nitrogenase of the blue-green alga Anabaena cylindrica

Abstract

Reduced ferredoxin was found to function as electron donor to nitrogenase present in extracts prepared from the blue-green alga Anabaena cylindrica. Two physiological mechanisms of reducing ferredoxin were identified. The major physiological mechanism of reducing ferredoxin was a process linked to the photosynthetic electron transport chain which was dependent on light. An alternative source of reducing potential was NADP + reduced in dark reaction by substrates such as isocitrate or pyruvate. Transfer of electrons from NADPH to nitrogenase was dependent on ferredoxin-NADP + reductase and ferredoxin.