Photosynthesis in a reconstituted chloroplast system from spinach. Some factors affecting CO2-dependent oxygen evolution with fructose-1,6-bisphosphate as substrate.

Abstract

When envelope-free spinach chloroplasts are incubated with stromal protein, catalytic NADP, catalytic ADP, radioactive bicarbonate and fructose 1,6-bisphosphate, 14CO2 fixation starts immediately upon illumination but oxygen evolution is delayed. The delay is increased by the addition of fructose 6-phosphate and by a variety of factors known (or believed) to increase fructose bisphosphatase activity (such as dithiothreitol, more alkaline pH, higher [Mg] and antimycin A). Conversely, the lag can be decreased or eliminated by the addition of an ATP-generating system. Bearing in mind the known inhibition, by ADP, of sn-phospho-3-glycerate (3-phosphoglycerate) reduction it is concluded that the lag in O2 evolution results from the production of ribulose 5-phosphate from fructose bisphosphate and that this in turn inhibits the reoxidation of NADPH by adversely affecting the ADP/ATP ratio. The results are discussed in their relation to the mode of action of antimycin A and to regulation of the reductive pentose phosphate pathway.