Properties of cell-free hydrogenases of Escherichia coli and Rhodospirillum rubrum.

The mechanism of conversion of substrate hydrogen to H2 in microbial fermentations is still obscure. One of the enzymes presumably involved in the final phase of H2 formation is hydrogenase, which catalyzes the reaction H2 =2H+ + 2e (Stephenson and Stickland, 1931). The present investigation was stimulated by our interest in the presumed participation of hydrogenase in photochemical production of H2 by photosynthetic bacteria and the apparent relationship of this enzyme to fixation of N2 in these organisms (Gest, Kamen, and Bregoff, 1950). Several properties of hydrogenase in cell-free preparations of Rhodospirillum rubrum, a photosynthetic N2-fixing organism, have been studied and are compared with the corresponding enzyme of the heterotrophic bacterium, Escherichia coli, which has thus far not been shown to fix N2 (Lindstrom, Lewis, and Pinsky, 1951).