SEPARATION BY MONOCHROMATIC LIGHT OF PHOTOSYNTHETIC PHOSPHORYLATION FROM OXYGEN EVOLUTION

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Abstract
To unmask the ferredoxin-dependent cyclic photophosphorylation and to demonstrate its independence from photoproduction of oxygen it was necessary to use special experimental devices such as far-red monochromatic light, anaerobic conditions, and inhibitors of oxygen evolution. However, if ferredoxin-dependent cyclic photophosphorylation is to be considered the cyclic photophosphorylation in vivo, then it must be shown that this type of photophosphorylation will also occur under the natural conditions of photosynthesis in leaves, i.e., in white light and in the presence of oxygen. The present findings and those reported earlier provide evidence that ferredoxin-dependent cyclic photophosphorylation by isolated chloroplasts is indeed compatible with these natural conditions of photosynthesis in leaves. Evidence for cyclic photophosphorylation in intact leaves, as distinguished from isolated chloroplasts, has recently been reported by Forti and Parisi. Work from several laboratories (most recently reviewed by Smith and French) has led to a now widely held view that photosynthesis in green plants involves the cooperation of at least 2 pigment systems, each of which carries on separate partial reactions essential to the over-all process. There is little biochemical evidence, however, as to which partial photochemical reaction is associated with which specific pigment system. The occurrence of ferredoxin-dependent cyclic photophosphorylation at 708 m[mu] and its independence from oxygen evolution is consistent with a hypothesis that, in chloroplasts, photophosphorylation (and TPN reduction) is dependent mainly on the chlorophyll a pigment system and hence can be experimentally separated from the photochemical activity of chlorophyll b, which is associated with photoproduction of oxygen.