Picó Guillermo, Bassani Georgina, Farruggia Beatriz, Nerli Bibiana
Bioseparation Lab, Physical-Chemistry Department, Faculty of Biochemical and Pharmaceutical Sciences, National University of Rosario, FonCyT, CIUNR and CONICET, Suipacha 570 (S2002RLK) Rosario, Argentina.
Int J Biol Macromol. 2007 Feb 20;40(3):268-75. doi: 10.1016/j.ijbiomac.2006.08.008. Epub 2006 Aug 22.
The binding of polyethyleneglycol of molecular mass 1000, 3300 and 6000 and polyethylene-propylene oxide (molecular mass 8400) to lysozyme and ovoalbumin was measured by isothermal calorimetric titration. A binding process was found to be associated with a saturation effect, which suggests a protein-polymer interaction. The proteins showed an affinity for the polymers in the order of 10(2)M(-1) and it decreased with the increase in the polymer molecular mass. The number of polymer molecules bound per protein molecule varied from 0.01 to 0.2 for polyethyleneglycol 1000, 3300 and polyethylene-polypolypropylene oxide 8400, while for polyethyleneglycol 6000 such number got closer to the unity. The enthalpic change associated with the binding was positive in the order of 1 kcal/mol for lysozyme, while ovoalbumin showed values around 2-3 kcal/mol. Entropic changes were also positive with values around 17-20 e.u. for ovoalbumin and 1-7 e.u. for lysozyme. The heat associated with the protein transfer from a buffer to a medium containing the polymer or the salt (a process similar to protein partitioning in aqueous two-phase systems) was obtained. These results allow the direct calculation of the enthalpic change associated with a protein partition process in aqueous two-phase systems without applying the van'tHoff equation. In this way, it is possible to calculate the associated true heat when the protein is transferred from the bottom to the top phase.
采用等温滴定量热法测定了分子量为1000、3300和6000的聚乙二醇以及聚环氧乙烷-聚环氧丙烷（分子量8400）与溶菌酶和卵清蛋白的结合情况。发现结合过程伴随着饱和效应，这表明存在蛋白质-聚合物相互作用。蛋白质对聚合物的亲和力顺序为10²M⁻¹，且随聚合物分子量的增加而降低。对于分子量为1000、3300的聚乙二醇以及分子量为8400的聚环氧乙烷-聚环氧丙烷，每个蛋白质分子结合的聚合物分子数在0.01至0.2之间，而对于分子量为6000的聚乙二醇，该数值更接近1。与溶菌酶结合相关的焓变约为1千卡/摩尔，呈正值，而卵清蛋白的焓变值约为2 - 3千卡/摩尔。熵变也为正值，卵清蛋白的熵变值约为17 - 20熵单位，溶菌酶的熵变值约为1 - 7熵单位。获得了蛋白质从缓冲液转移至含有聚合物或盐的介质中时的热效应（这一过程类似于蛋白质在水相双相系统中的分配）。这些结果使得无需应用范特霍夫方程就能直接计算与蛋白质在水相双相系统中分配过程相关的焓变。通过这种方式，当蛋白质从下相转移至上相时，就有可能计算出相关的真实热效应。
