Abstract: Nattokinase, a new kind of food fibrinolytic enzyme, extracted from the Japanese traditional food natto, is foundto be a strong fibrinolytic enzyme. Compared with some traditional thrombolytics, nattokinase, is found to be safe and low-cost. The chemical modification has become an effective method to improve nattokinase activity. The experiments has obtained the optimum concentration of metal ion for nattokinase chemical modification. The 6mmol/L Mg2+ can obviously activate the modified NK 45% higher activity than the natural NK. Howerer the Ca2+, Mn2+ or Ni2+ can inhibit the NK activity to different extents.

Key words: nattokinase, metal ion, chemical modification