Terminal Effect of Drop Coalescence on Single Drop Mass Transfer Measurements and Its Minimization

For the mass transfer to single drops during the stage of steady buoyancy-driven motion, experimental measurement is complicated with the terminal effect of additional mass transfer during drop formation and coalescence at the drop collector. Analysis reveals that consistent operating conditions and experimental procedure are of critical significance for minimizing the terminal effect of drop coalescence on the accuracy of mass transfer measurements. The novel design of a totally-closed extraction column is proposed for this purpose, which guarantees that the volumetric rate of drop phase injection is exactly equal to that of withdrawal of drops. Tests in two extraction systems demonstrate that the experimental repeatability is improved greatly and the terminal effect of mass transfer during drop coalescence is brought well under control.

黑曲霉糖化酶cis调控区上两个CCAAT框协同参与基因启动子的转录激活作用

已报道的EMSA和Footprinting试验表明黑曲霉Aspergillus niger T21糖化酶基因glaA启动子区-489～-414bp及-390～-345bp(分别简称为DC,PC)是与蛋白粗提液中同一蛋白因子结合,并均含有CCAAT五核苷酸的序列。对DC,PC在糖化酶表达调控中的作用进行了分析,用CGTAA取代CCAAT,获得突变体DCm,PCm,两者均丧失体外结合蛋白因子的能力。突变体的体内分析结果显示,DC和PC中任何一个发生突变或改变DC,PC在原启动子中的相对方向,则启动子的活性下降到基础表达水平,将多拷贝串联后的DC引入A.niger T21glaA启动子原位,则内源糖化酶的表达和由该启动子引导的外源uidA基因的表达均发生下降,但由构巢曲霉3-磷酸甘油醛脱氢酶启动子PgpdA引导的uidA的表达不受影响,而且EMSA结果表明不等DC拷贝的A.niger转化子中DNA结合蛋白的含量没有明显变化,表明多拷贝DC的引入引起了调控蛋白的滴定效应,从A.niger T21cDNA中克隆到AngHapC基因,将AngHapC基因引入上述含多拷贝DC而糖化酶低表达的A.niger菌株,AngHapC基因的表达使糖化酶的表达量得到明显回升。上述结果表明,DC和PC中CCAAT五核苷酸序列为蛋白因子结合所必需,而且两者必须同时与调控蛋白结合才能发挥促进转录的作用,AngHapC为与DC区域结合的正调节蛋白。