Stability and conformational change of methoxypolyethylene glycol modification for native and unfolded trypsin

The effect of succinimidyl carbonates activated methoxypolyethylene glycol (mPEG-SC) on the catalytic properties and conformation of native trypsin and dynamic high-pressure microfluidisation (DHPM) induced unfolded trypsin was studied. The thermal stability of unfolded trypsin was enhanced more significantly than that of native trypsin between 45 and 70 °C. The autolysis analysis indicated that modified unfolded trypsin was markedly more resistant to autolysis compared to modified native trypsin between 40 and 180 min. Upon mPEG-SC conjugation, the Km value of the enzyme decreased by about 2-fold, and the catalytic efficiency (Kcat/Km) increased by about 3-4-fold. Moreover, the increased thermal stability of unfolded trypsin might be due to the lower surface hydrophobicity and the higher hydrogen bond formation after mPEG-SC modification, which was reflected in the decrease of UV absorbance, the quenching and blue shift of fluorescence spectra, as well as the increase of β-sheet content.