Spectroscopic characterization of ferredoxin from the blue-green alga Microcystis flos-aquae

Ferredoxins have been isolated as components of the photosynthetic systems of a very wide range of organisms from the anaerobic green and purple photosynthetic bacteria to the higher plants (see Hall & Evans, 1969; Buchanan & Amon, 1970). All these ferredoxins have very low redox potentials close to that of hydrogen (E'=420mV), and are interchangeable to some extent in biological activity. The ferredoxins from higher plants are the best charac- terized; they have molecular weights about 11000, contain two atoms each of Fe and labile sulphide/ molecule, and accept one electron on reduction. The ferredoxins of photosynthetic bacteria are less well characterized, but seem to be similar to those of the anaerobic fermentative bacteria, which contain eight atoms each of Fe and labile sulphide/molecule and accept two electrons. In the photosynthetic bacteria the ferredoxins also appear to be involved in fixation of atmospheric N2 (Evans & Smith, 1971).