Abstract: Positively charged Bacillus subtilis neutral proteinase dissolved in the aqueous phase at a pH value below its pI could form hydrophobic ion-pair with the anionic surfactant AOT in isooctane when they are mixed together due to electrostatic attraction. Thus，the hydrophilic enzyme could be “solubilized” into the hydrophobic isooctane. In this paper，the factors affecting the ion pair formation were investigated，such as，mixing conditions of the two phases，initial pH value and ionic strength，salts，the concentrations of the enzyme and surfactant AOT. The results indicated that magnetic stirring at 120r/min for 6 h was better than other mixing methods. The initial pH value of the aqueous phase affected both formation of enzyme-surfactant ion pair and transfer of the enzyme into isooctane. The optimal pH value was about 5.0. Addition of CaCl2 could partially prevent emulsifying during mixing，but excessive CaCl2 could negatively affect formation of ion pair and transfer of the enzyme from aqueous phase into isooctane. The transferred amount of enzyme into isooctane increased when AOT concentration increased within the limit (below the critical concentration of reverse micelle formation，4.9 mmol/L)，although the initial concentration of the enzyme in the aqueous phase was kept constant. However，with a constant AOT in isooctane，the enzyme transfer increased with increasing initial concentration of the enzyme in the aqueous phase first but decreased with further increase. The results showed that Bacillus subtilis neutral proteinase extracted into the organic phase was still active and could catalyze the transesterification.

摘要： 枯草杆菌蛋白酶在水相pH值小于其等电点条件下带正电，能与异辛烷中带负电的阴离子表面活性剂二辛基丁二酸磺酸钠（AOT）通过静电引力结合形成离子对进入有机相。详细研究了两相接触方式、水相初始pH值、水相离子强度等因素对酶转移率的影响。采用120 r/min磁力搅拌使两相混合能得到较好的酶转移率，作用时间为6 h。水相初始pH值5.0有利于离子对的形成及酶蛋白的转移。水相中CaCl2的加入有利于消除两相混合过程中的乳化；但是过高的CaCl2浓度会减弱酶分子与AOT间的静电引力，不利于酶分子与AOT的结合。水相中酶浓度不变，随着有机相中AOT初始浓度的增加，酶的转移率呈现增长趋势。固定异辛烷中AOT浓度，随着水相中初始酶浓度的增加，转移至有机相中酶量先增加后减少。进入异辛烷的酶分子仍旧保持活性，能催化转酯化反应的进行，但随着反应时间的延长，酶的催化效率出现下降。