Abstract: Arabidopsis thaliana superoxide dismutase 1(AtSOD1) has been considered as a critical protein conferring cellular protection against the excessive accumulation of toxic reactive oxygen species, and an ideal model enzyme to understand the relationship between the structure and function of the protein as well. However, the structure stability and catalytic property of AtSOD1 remain poorly understood. In this research, active AtSOD1 with the correct coordinated geometry proved by electron paramagnetic resonance (EPR) was heterogeneous expressed in Escherichia Coli (Rosseta), and then the thermal stability of the enzyme was further analyzed. Urea denaturation of apo and holo AtSOD1 was monitored by circular dichroism (CD), and the results indicated that there was a curve point between α-helix and β-fold in 0-8 mol/L urea while performance at 225 nm wave length. In addition, the curvilinear plateau had been found in holo AtSOD1 when added urea concentration increased from 4 to 5 mol/L. Interestingly, the trace of differential scanning calorimetry (DSC) heating scan of the holo enzyme indicated that the exothermic transition temperature (Tm) value had been observed at 102.2 ℃ and 100.5 ℃ in the enzyme reconstruction from monomer to dimer. According to the CD and DSC results, it was speculated that there is an intermediate state in the dimer unfolding process of AtSOD1 which reflects a type of special structure concerned structure stability.

Key words: copper-zinc superoxide dismutase, protein dimer, differential scanning calorimetry