The Ratio of RuBP Carboxylase to Oxygenase Activity and Photosynthetic Gas Exchange

Photosynthetic CO2 uptake and photorespiratory CO2 release of C3-leaves are related to the reactions catalyzed by the enzyme ribulose bis-phosphate carboxylase oxygenase (RuBPCO), whereby photosynthetic CO2 uptake corresponds to the carboxylase and photorespiratory CO2 release to the oxygenase activity of the enzyme. The ratio of photosynthetic CO2 uptake to photorespiratory CO2 release increases as temperature is decreased. This has been attributed to a change in the solubility ratio of CO2 to O2 (1.) and to a change in the ratio of the activity of carboxylase to oxygenase (2). This would mean that photosynthetic gas exchange is fully explained by RuBPCO kinetics. Our experiments, presented here, do not support this view.