The nitrogen fixation system of photosynthetic bacteria. I. Preparation and properties of a cell-free extract from Chromatium

Abstract

The preparation and properties of cell-free extracts of the photosynthetic bacterium Chromatium which give consistent and appreciable nitrogen fixation are described. Nitrogen fixation required ATP and reducing power. Reducing power was supplied by reduced ferredoxin or, in its absence, by sodium dithionite or H 2, in the presence of catalytic amounts of a viologen dye. ATP was supplied by phosphocreatine and creatine phosphokinase, with a catalytic amount of free ATP. The Chromatium nitrogenase complex was found to have the typical properties of other nitrogenases, i.e., reduction of N 2 to ammonia, and of acetylene to ethylene, ATP-dependent H 2 evolution and reductant-dependent ATP hydrolysis.