[Properties of two forms of ferredoxin from Rhodopseudomonas capsulata]

Electrophoretically homogenous preparations of two forms of ferredoxin were isolated from the nitrogen-fixing cells of the purple non-sulphur bacterium Rhodopseudomonas capsulata B10. The values of Mr for ferredoxins I and II are 12000 and 18000, respectively. Ferredoxin I contains 8 atoms of Fe+2 and 8 atoms of S2-; ferredoxin II--4 atoms of Fe2+ and 4 atoms of S2- per molecule. The ferredoxins differ also in their absorption spectra, stability and catalytic activity during electron transfer to nitrogenase of Rh. capsulata. The reduction of C2H2 and evolution of H2 in the presence of ferredoxin I occurs twice as fast as compared to that in the presence of ferredoxin II. Ferredoxin I synthesis takes place in the nitrogen-fixing cells of Rh. capsulata alone, whereas ferredoxin II formation does not depend on the growth conditions.