Delgado C, Malik F, Selisko B, Fisher D, Francis G E
Molecular Cell Pathology Laboratory, Royal Free Hospital School of Medicine, London, UK.
J Biochem Biophys Methods. 1994 Dec;29(3-4):237-50. doi: 10.1016/0165-022x(94)90035-3.
Covalent attachment of poly(ethylene glycol) (PEG) to proteins produces conjugates with altered/improved physicochemical and biological properties which depend upon the number of PEG chains linked. Quantification of the attached PEG is however not a trivial issue. The partition coefficient, K, of the PEG-protein conjugate in PEG/dextran two-phase systems provides a quantitative measure for the degree of modification. A linear relationship between log K and the number of PEG chains was observed in fractionated PEG-modified-granulocyte-macrophage colony stimulating factor conjugates having 1 to 3 substitutions. Furthermore, in mixtures of PEG-bovine-serum-albumin conjugates with increasing degrees of modification, a linear relationship was found between log K and n, the average substitution. The increment in log K per PEG chain added is protein specific and this suggests that the interactions between the PEG-protein conjugate and the polymers in the phase system are more complex than just a simple affinity of the PEG for the PEG-rich top phase. Increasing the polymer concentration in the phase system produces larger increments in log K per PEG molecule attached and the proportionality between log K and number of PEG molecules is only compromised for conjugates with high degree of substitution when partitioned in biphasic systems of high concentration of polymers.
聚乙二醇（PEG）与蛋白质的共价连接产生具有改变/改善的物理化学和生物学性质的缀合物，这些性质取决于连接的PEG链的数量。然而，对连接的PEG进行定量并非易事。PEG/葡聚糖双相系统中PEG-蛋白质缀合物的分配系数K提供了修饰程度的定量测量。在具有1至3个取代的分级PEG修饰的粒细胞-巨噬细胞集落刺激因子缀合物中，观察到log K与PEG链数量之间的线性关系。此外，在修饰程度增加的PEG-牛血清白蛋白缀合物混合物中，发现log K与平均取代度n之间存在线性关系。每个添加的PEG链的log K增量是蛋白质特异性的，这表明PEG-蛋白质缀合物与相系统中的聚合物之间的相互作用比仅仅是PEG对富含PEG的上相的简单亲和力更为复杂。增加相系统中的聚合物浓度会使每个连接的PEG分子的log K产生更大的增量，并且当在高浓度聚合物的双相系统中分配时，log K与PEG分子数量之间的比例仅在高取代度的缀合物中受到影响。
