Mechanism of Biological Nitrogen Fixation X. Hydrogenase in Cell-free Extracts and Intact Cells of Azotobacter*

The discovery of hydrogenase in Azotobacter cells (1) raises the question of its function in the metabolism of this organism. This enzyme is usually found in anaerobic or facultative anaerobic bacteria which liberate Hz from certain substrates. Azotobacter is a strict aerobe, and its metabolism consists primarily in the simple oxidation of substrate to carbon dioxide and water. Although not conclusive, certain observations to be discussed later suggest that hydrogenase may be related to the nitrogen fixation enzyme system in Axotobacter. Demonstration of such a relationship would provide new insight into many aspects of the mechanism of the reaction including the chemical pathway. Our previous investigations on this question have been carried out entirely with resting suspensions of the organism, but for certain studies a cell-free preparation would be advantageous. The preparation and properties of a cell-free extract from Axotobacter containing hydrogenase are described in this report.