Dithiothreitol decreases the thermal stability and unfolding coperativity of ribulose-1, 5-bisphosphate carboxylase/oxygenase

Plant rubisco consists of eight large subunits (55 kD) encoded by chloroplast gene and eight small subunits (15 kD) encoded by nuclear gene. There are abundant cysteine residues that do not form disulfide bonds in native rubisco. Differential scanning calorimetry has been used to study some plant rubisco and suggested an irreversible two-state denaturation due to the high cooperativity in subunits. By comparing the data from circular dichroism, fluorescence, differential scanning calorimetry, SDS electrophoresis, and activity assays in the absence or presence of DTT, we suggest that the formation of disulfide bonds in subunits during the early thermal unfolding may increase the thermal stability and the thermal unfolding cooperativity of rubisco.