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Autocatalysis in a Reconstituted Chloroplast System ¹

^a Department of Botany, The University of Sheffield, Sheffield, England

In whole plants and intact chloroplasts, photosynthesis does not reach its full rate immediately upon illumination but only after a lag which is believed to reflect an autocatalytic increase in the concentration of carbon cycle intermediates. Autocatalysis has now been observed in a reconstituted system containing envelope-free chloroplasts augmented with ferredoxin and other stromal proteins but only catalytic amounts of ATP and NADP. With ribose 5-phosphate as substrate, the CO₂ dependent O₂ evolution recorded for such mixtures implies rates of "endogenous" or ferredoxin-dependent photophosphorylation as high as 360 µmoles of orthophosphate esterified mg^–1 chlorophyll hr^–1.