Evidence was obtained indicating that the superoxide dismutase (SOD) A and B isoenzymes of the wheat cultivar Tonic are of the Cu/ Zn type, whereas the SOD-C group are similar to manganese containing dismutases. Heat inactivation plots showed that the enzymic activity in crude extracts was relatively stable up to 50°C. The thermodynamic parameters enthalpy, ΔH#, free energy, ΔG#, and entropy, ΔS#, were estimated for the thermal inactivation of extracted SOD activity and a purified SOD-C isoenzyme. The SOD-C isoenzyme was purified extensively and shown to contain two closely related tetrametic isozymes (pI6·0 and 66·1) of Mr 80 000. A Mr of 20 000 has been calculated for the subunits. The N-terminal amino acid sequence of the purified SOD-C could be aligned with that of the Mn-SOD enzyme of maize and showed 57% homology.
- Heat inactivation
- Superoxide dismutase