Association of Heat-Induced Conformational Change with Activity Loss of Rubisco

Abstract Circular dichroism (CD), fluorescence, and differential scanning calorimetry (DSC) were used to investigate the thermal conformational change associated with the activity loss of spinach Rubisco. CD and intrinsic fluorescence demonstrated a three stage thermal unfolding of Rubisco. At 25–45°C, the secondary structure did not change but the tertiary and/or quaternary structure changed obviously with increased temperature. In 45–60°C, the secondary structure showed much change with increased temperature and the tertiary and/or quaternary structure changed much faster. Over 60°C, whole conformation changed abruptly with increased temperature and finally unfolded completely. DSC, CD and activity assays after annealing showed that the conformational change and the activity loss of Rubisco were completely reversible if the heating temperature was below 45°C, partly reversible between 45 and 60°C, and irreversible beyond 60°C.