DMSO对鸡蛋白溶菌酶溶液变性的影响

摘要

A study on thermal denaturation of hen egg-white lysozyme (HEWL) was carried out by differential scanning calorimetry (DSC) and modulated temperature differential scanning calorimetry (MDSC). It was found that DSC profiles of HEWL were dependent on heating rates and concentrations of enzyme as well as cosolvent. The enthalpy of denaturation (△Hm) increased with increasing enzyme concentration in aqueous solution. In aqueous solution containing dimethylsolfoxide (DMSO), denaturation temperature (Tm) shifted toward lower temperature, and the transition peak became shallower and broader with increasing volume proportion of DMSO. When the content of DMSO was more than 70 %, only a declining smooth line could be observed instead of a single endothermic transition curve.Interestingly, from MDSC curves of HEWL in aqueous solution without DMSO, a small and symmetrical peak in front of the main transition (Ⅰ) was observed marginally, which was regarded as a pre-transition (Ⅱ). Specially, this small and marginal peak could not be found in aqueous solution containing DMSO. In addition, with increasing amount of protein, Tm(Ⅱ) shifted toward lower temperature, and △Hm(Ⅱ) decreased along with the temperature gap between two transitions lengthened. The results were considered to be due to the reversible dissociation of HEWL dimers in aqueous solution.%利用差示扫描量热(DSC)和温度调制差示扫描量热(MDSC)研究了鸡蛋白溶菌酶在纯水及二甲基亚砜(DMSO)/水混合溶剂中的热变性过程,探讨了酶的浓度、扫描速率和共溶剂的含量对热变性行为的影响规律.在纯水溶液中,溶菌酶的变性焓(△Hm)随酶浓度的增大而增大.而在DMSO/水混合溶剂中,变性温度(Tm)随DMSO体积分数的增大向低温方向移动,变性峰变低变宽;当DMSO体积分数达到70%后,热变性曲线变成了一条光滑的直线.另外,在纯水溶液中溶菌酶的MDSC图除了出现DSC中可观察到的主吸热峰(Ⅰ)外,在峰(Ⅰ)的前面还出现一个小而对称的吸热峰(Ⅱ),并且当体系中有DMSO存在时也未能观察到此峰.当溶菌酶浓度增大时,Tm(Ⅱ)移向低温,△Hm(Ⅱ)减小,Tm(Ⅰ)与Tm(Ⅱ)之间的距离变长.吸热峰(Ⅰ)的出现被认为是由于水溶液中溶菌酶二聚体的可逆离解造成的.