Abstract:

Zinger protease was modified separately with monomethoxypolyethylene glycol (mPEG) and dextran to promote its activity and stability. Dextran and mPEG were activated by sodium periodate and by cyanuric chloride, respectively. The activated mPEG and dextran were solely added into sodium tetraborate buffer solution with 2.0 mg/mL zinger protease and then the mixed solutions were incubated at 40 ℃ for 1 h. The optimal mass ratio between modifying agent and zinger protease, and reaction pH were measured. When the ratio between mPEG and zinger protease was 17.5:1.0 and pH was 9.0, the modification rate of zinger protease modified with mPEG was 52.6% and the relative enzyme activity (activity of modified enzyme/activity of natural enzyme) was 54.0%. The modification rate of zinger protease modified with dextran was 51.6% and the relative enzyme activity was 3.3 at the conditions of dextran/zinger protease ratio of 42:1 and pH 6. The thermal stability of both modified enzymes was higher than that of natural enzymes; meanwhile, the thermal stability of zinger protease modified with dextran was higher than that of zinger protease modified with mPEG. Therefore, dextran has a better modification effect on zinger protease than mPEG. Dextran is more suitable for the chemical modification of proteases and the development and utilization of novel enzymes.

Key words: zinger protease, monomethoxypolyethylene glycol, dextran, chemical modification