Abstract:Polysialic acid(PSA) is considered an ideal alternative material of the polyethylene glycol(PEG) for protein or peptide modification due to its more effective safety in therapeutics.This research was a preliminary study of modification of CuZn superoxide dismutase(CuZn-SOD) with polysialic acid.The optimal conditions for the modifying reaction were as follows: PSA was activated by periodate oxidation,then coupled to CuZn-SOD in the PSA: SOD mole ratios of 40: 1 for 24h.It was shown that polysialylated macromolecule contained 3.9±0.3 molecules of PSA per molecule of SOD.SDS-PAGE electrophoresis and Atomic Force Microscopy(AFM) revealed that the molecular weight of polysialylated SOD was about 90~100kDa and the average size was 10~15nm,about four-fold of native enzyme size.Besides,it showed two kinds of microscopic spherical shape: coated single particle or coated multiple particles.As compared with native enzyme,the stabilities of modified enzyme against heat,acid,alkali and proteinases such as pepsin and trypsin were improved significantly.
