Stability and identification of active-site residues of carboxymethylcellulases from Aspergillus niger and Cellulomonas biazotea
Stability and identification of active-site residues of carboxymethylcellulases from Aspergillus niger and Cellulomonas biazotea
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DOI：
10.1007/bf02816941
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发表时间：
1997-01-01
影响因子：
2.6
通讯作者：
Rajoka, MJ
中科院分区：
文献类型：
--
作者：
Siddiqui, KS;Azhar, MJ;Rajoka, MJ
从黑曲霉和双氮胞单胞菌中分离得到的羧甲基纤维素酶在不同温度和二氧六环存在下的表观pk(a) s测定表明，两种生物体内有两个侧链羧基控制其极限速率，两种酶的热稳定性随pH从5增加到7.5略有下降，但在0.5 mmol/L Mn2+的存在下不受影响。在8 mol/L尿素存在下，40℃条件下，黑曲菌CMCase的活化能为35 kJ/mol，半衰期为89 min；在8 mol/L尿素和37℃条件下，用0 ~ 9 mol/L尿素横向梯度PAGE测定的CMCase的半衰期为125 min。在没有CMC的情况下，来自黑曲霉和双偶氮梭菌的cmcase具有相同的热稳定性，尽管来自农民的酶在有底物的情况下具有更强的热稳定性。黑曲霉的CMCase水解CMC的效率也高于双偶氮酸梭菌。
Determination of the apparent pk(a)'s of purified carboxymethylcellulases from Aspergillus niger and Cellulomonas biazotea at different temperatures and in the presence of dioxane indicated two side chain carboxyl groups which controlled the limiting rate in both organisms, The thermostability of both enzymes slightly decreased with increasing pH from 5 to 7.5 but was unaffected in the presence of 0.5 mmol/L Mn2+. The CMCase from C. biazotea had an activation energy of 35 kJ/mol and a half-life of 89 min in the presence of 8 mol/L urea at 40 degrees C. The half-life of CMCase from A. niger in 8 mol/L urea and at 37 degrees C was 125 min as determined by a 0-9 mol/L transverse urea gradient PAGE. The CMCases from A. niger and C. biazotea had the same thermostabilities in the absence of CMC although the enzyme from the farmer was more thermostable in the presence of the substrate. The CMCase from A. niger was also more efficient in hydrolyzing CMC than the enzyme from C. biazotea.