Regulation of Ribulose Bisphosphate Carboxylase Activity in Intact Wheat Leaves by Light, CO2, and Temperature

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Abstract
The activity of the enzyme ribulose bisphosphate carboxylase (RuBPCase) was estimated after rapidly extracting it from intact wheat leaves pretreated under different light and CO2 levels. No HCO3− was added to the extraction buffer since it is shown to inhibit RuBPCase. The activity increased as light intensity or CO2 concentration during pretreatment was increased. Enzyme activity increased as temperature during pretreatment was decreased. Light activation did not affect the affinity of RuBPCase for CO2. A Km of 30 μM CO2 under air level O2 was determined. CO2, light and temperature are three main limiting factors of photosynthesis. It seems that the activity of RuBPCase is regulated by these factors according to the requirements for CO2 fixation.