Characterization and stability investigation of cu,zn-superoxide dismutase covalently modified by low molecular...

Cu,Zn-superoxide dismutase (SOD) was chemically modified with low molecular weight heparin (LMWH). To characterize the conjugate, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and native polyacrylamide gel electrophoresis (native PAGE) with protein staining and polysaccharide staining were employed. The stabilities of the modified enzyme to heat, acid, alkali, and trypsin treatment were also investigated. SDS-PAGE of the conjugate presented two major bands, and native PAGE of the conjugate showed similar banding position with protein staining and polysaccharide staining, which was different from that of the unmodified SOD and LMWH/SOD mixture. Moreover, the conjugate migrated faster with increasing extent of the modification. Enhanced heat stability, acid resistance, alkali resistance, and anti-trypsin stability of the modified enzyme were observed compared with those of the unmodified enzyme. Results of the study suggest that covalent linkage in LMWH-SOD can be effectively characterized by electrophoretic techniques and the chemical modification of SOD with LMWH can enhance the stabilities of the enzyme. In addition, native PAGE with protein staining can be used to evaluate the extent of the modification.