N-Acetyl-β-D-glucosaminidase（NAGase, EC 3.2.1.52）, which catalyzes the cleavage of N-acetylgluco- samine polymers, plays important roles in the molting, digestion of chitinous foods in green crab. In the study, the...N-Acetyl-β-D-glucosaminidase（NAGase, EC 3.2.1.52）, which catalyzes the cleavage of N-acetylgluco- samine polymers, plays important roles in the molting, digestion of chitinous foods in green crab. In the study, the efforts of urea on the activity of NAGase purified from the viscera of green crab（Scylla serrata） have been studied. The results show that appropriate concentrations of urea can lead to reversible inactivation of the enzyme, and the value of the inhibitor concentration leading to 50% of enzyme activity lost（IC50） is estimated to be 0.63 mol/L. The inactivation kinetics has been studied via the kinetic method of the substrate reaction. The rate constants of inactivation have been determined. The value of k＋0 is larger than that of k′＋0, indicating the free enzyme molecule is more fragile than the enzyme-substrate complex in urea solution. It is suggested that the presence of the substrate offers the marked protection of this enzyme against inactivation by urea.展开更多
The effects of some sugars(glucose,mannose,fructose,sucrose and chitosan)and polyols(glycol,gly-cerol and sorbitol)as protective additive on the thermo-stability ofβ-mannanase were studied.The optimal reaction temper...The effects of some sugars(glucose,mannose,fructose,sucrose and chitosan)and polyols(glycol,gly-cerol and sorbitol)as protective additive on the thermo-stability ofβ-mannanase were studied.The optimal reaction temperatures ofβ-mannanase and the ther-modynamics and the deactivation kinetics with or without additives were also investigated.The experimental results show that sucrose,chitosan and sorbitol could apparently improve the thermal stability ofβ-mannanase when their concentration was kept at 2 g/L.The optimal combina-tion additive proportion was sucrose:chitosan:sorbi-tol=1:2:2(molar ratio)using the orthogonal experimental design.The sucrose,chitosan,glycerol,sor-bitol and the combination additive might increase the optimal reaction temperature from 50℃to about 60℃due to their good protection effect.The thermal deactiva-tion curves ofβmannanase accorded with the kinetic rules of first order reaction,and the corresponding kinetic and thermodynamic parameters were calculated.Meanwhile,the protective mechanism of the additives against deactivation of enzyme was also discussed.展开更多
基金Supported by the National Natural Science Foundation of China(No.40576066)the Science and Technology Foundation of Xiamen,China(No.3502Z20081143)
文摘N-Acetyl-β-D-glucosaminidase（NAGase, EC 3.2.1.52）, which catalyzes the cleavage of N-acetylgluco- samine polymers, plays important roles in the molting, digestion of chitinous foods in green crab. In the study, the efforts of urea on the activity of NAGase purified from the viscera of green crab（Scylla serrata） have been studied. The results show that appropriate concentrations of urea can lead to reversible inactivation of the enzyme, and the value of the inhibitor concentration leading to 50% of enzyme activity lost（IC50） is estimated to be 0.63 mol/L. The inactivation kinetics has been studied via the kinetic method of the substrate reaction. The rate constants of inactivation have been determined. The value of k＋0 is larger than that of k′＋0, indicating the free enzyme molecule is more fragile than the enzyme-substrate complex in urea solution. It is suggested that the presence of the substrate offers the marked protection of this enzyme against inactivation by urea.
基金supported by the Tianjin Science&Technology Commission of China(No.05YFGZGX04600)the National Key Technology R&D Program(No.2007BAD42B02)the International Science and Technology Cooperation Program(No.2006DA62400).
文摘The effects of some sugars(glucose,mannose,fructose,sucrose and chitosan)and polyols(glycol,gly-cerol and sorbitol)as protective additive on the thermo-stability ofβ-mannanase were studied.The optimal reaction temperatures ofβ-mannanase and the ther-modynamics and the deactivation kinetics with or without additives were also investigated.The experimental results show that sucrose,chitosan and sorbitol could apparently improve the thermal stability ofβ-mannanase when their concentration was kept at 2 g/L.The optimal combina-tion additive proportion was sucrose:chitosan:sorbi-tol=1:2:2(molar ratio)using the orthogonal experimental design.The sucrose,chitosan,glycerol,sor-bitol and the combination additive might increase the optimal reaction temperature from 50℃to about 60℃due to their good protection effect.The thermal deactiva-tion curves ofβmannanase accorded with the kinetic rules of first order reaction,and the corresponding kinetic and thermodynamic parameters were calculated.Meanwhile,the protective mechanism of the additives against deactivation of enzyme was also discussed.
