Methods for in vivo measurement of the concentration of the reactive centers of ribulose-1,5,-bisphosphate carboxylase/oxygenase (Rubisco) are suggested that are based on saturation of the active centers with RuBP and determination of the concentration of the Rubisco–RuBP complex. The total concentration of potentially reactive centers is calculated from the dependence of the concentration of this complex on CO2 concentration at a steady-state photosynthetic rate with further extrapolation of the carbon dioxide dependence curve to a zero CO2 concentration. The concentration of centers that possessed a catalytic activity under given environmental conditions was measured after transferring leaves having a steady-state photosynthetic rate into a medium devoid of CO2 and O2. This procedure ensured the saturation of the carboxylation centers with RuBP. The carboxylation rates were measured during a short-term exposure to 14CO2, and the concentration of the complex was calculated using the values of CO2 concentration during the exposure time, as well as the carboxylation rate and constant. Rubisco activity was found to decrease at elevated CO2 concentrations due to a lower concentration of catalytically active enzyme centers.
Russian Journal of Plant Physiology – Springer Journals
Published: Oct 10, 2004
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