ATP-Dependent hydrogen evolution by cell-free preparations of Azotobacter Vinelandii

Abstract

1.The ATP-dependent evolution of H2 catalyzed by cell-free preparations of N2-grown A. vinelandii was examined. The reaction required hydrosulfite and Mg2+ as well as ATP. Optimal reaction conditions were determined. The enzyme preparations were stable in air for several days when stored at 0°.2.A distinction was made between the enzyme catalyzing ATP-dependent H2 evolution and that catalyzing H2 uptake associated with the reduction of methylene blue and ferricyanide. H2 evolution was limited to preparations of cells grown on nitrogen-free medium and could not be demonstrated with extracts of urea-grown cells; H2 uptake was catalyzed by extracts of both N2− and urea-grown cells. H2 evolution was associated with material sedimented between 1-and 6-h centrifugation at 144 000 × g; H2 uptake activity was associated with more readily sedimented material. Heating the extracts at 60° for 15 min destroyed H2 uptake activity but had little effect on H2 evolution activity. It was concluded that the two reactions were catalyzed by different enzymes.