金属离子对锯缘青蟹NAGase活力的影响

Effects of metal ions on the activity of N-acetyl-β-Dglucosaminidase from green crab(Scylla serrata)

本文研究了几种金属离子对锯缘青蟹(Scylla serrata)N-乙酰-β-D-氨基葡萄糖苷酶(NAGase)活力的影响.其结果表明:Li+、Na+和K+对酶活力没有明显影响,Mg2+、Ca2+和Ba2+对该酶均有激活作用,激活程度依次为Ca2+>Ba2+>Mg2+.A l3+、Fe3+、Cd2+、Pb2+和Hg2+对该酶具有一定的抑制作用,2.0μmol/dm3的Hg2+可以使酶活力完全丧失.Co2+对酶的效应是先激活后抑制,Mn2+对酶仅有轻微的激活作用.Cd2+和Fe3+对锯缘青蟹NAGase的抑制作用都呈竞争性-反竞争性混合Ⅱ型效应,Cd2+的抑制常数KI和KIS分别为23.9、5.0 mmol/dm3,Fe3+的抑制常数KI和KIS分别为395.5、135.6μmol/dm3.KI>KIS,说明酶-底物络合物(ES)与抑制剂的亲和力比游离酶(E)与抑制剂的亲和力大.

The effects of some metal ions on the activity of N-acetyl-β-D-glucosaminidase （NAGase） from green crab （Scylla serrata） have been studied and the results show that Li^＋ , Na^＋ and K^＋ have no effect on the enzyme activity; Mg^2＋ , Ca^2＋ and Ba^2＋ activate the enzyme with an order of Ca^2＋ 〉 Ba^2＋ 〉 Mg^2＋ in intensity, while Al^3＋ , Fe^3＋ , Cd^2＋ , Pb^2＋ and Hg^2＋ inhibit the enzyme activity. 2. 0μmol/dm^3 of Hg^2＋ decreases the enzyme activity completely. Co^2＋ activates the enzyme at concentration lower than 4. 0 mmol/dm^3 but inhibits it at higher concentration. Mn^2＋ has a little active effects on the enzyme. Inhibitory kinetics of Cd^2＋ and Fe^3＋ on the enzyme has beea studied. It shows that the inhibition type of Cd^2＋ and Fe^3＋on the enzyme is of mix-typed Ⅱ. The combination constants of Cd^2＋ and Fe^3＋ with free enzyme （ KI） and enzyme-substrate complex （ KIS ） were determined respectively. The values of KI and KIS are abtained as 23.9 and 5. Ommol/dm^3 for Cd^2＋ and 395.5 and 135.6μmol/dm^3 for Fe^3＋ , respectively. K, is larger than K,s, which elucidates that Cd^2＋ and Fe^3＋ inhibit enzyme-substrate complex much potently than free enzyme.