Polyelectrolyte-protein interaction mechanism

High sorption capacities with respect to protein macromolecules are observed when highly permeable macro- and heteroreticular polyelectrolytes (biosorbents) are used. In buffer solutions a typical picture of interaction between ions with opposite charges fixed on CP and counterions in solution is observed. As shown in Fig. 13, in the acid range proteins are not bonded by carboxylic CP because the ionization of their ionogenic groups is suppressed. The amount of bound protein decreases at high pH values of the solution because dipolar ions proteins are transformed into polyanions and electrostatic repulsion is operative. The sorption maximum is either near the isoelectric point of the protein or depends on the ratio of the pi of the protein to the pKa=0 5 of the carboxylic polyelectrolyte [63]. It should be noted that this picture may be profoundly affected by the mechanism of interaction between CP and dipolar ions similar to that describedby Eq. (3.7). 

From the physics point of view, the system that we deal with here—a semiflexible polyelectrolyte that is packaged by protein complexes regularly spaced along its contour—is of a complexity that still allows the application of analytical and numerical models. For quantitative prediction of chromatin properties from such models, certain physical parameters must be known such as the dimensions of the nucleosomes and DNA, their surface charge, interactions, and mechanical flexibility. Current structural research on chromatin, oligonucleosomes, and DNA has brought us into a position where many such elementary physical parameters are known. Thus, our understanding of the components of the chromatin fiber is now at a level where predictions of physical properties of the fiber are possible and can be experimentally tested. 

Mixed retention mechanisms are most evident in the separation of polyelectrolytes. These are large, multivalent molecules, which possess polar and non-polar groups (or sites ) on the surface of the molecule in solution, that may interact physically with the backbone of the ion-exchanger. The most important examples of polyelectrolytes are proteins. 1EC has long been the major tool for the separation of proteins by HPLC, but it is being replaced more and more by RPLC [344]. One of the reasons for this is that due to mixed retention mechanisms broad and non-symmetrical peaks are common for the 1EC separation of proteins. 

Anionic polyelectrolytes have been used in the development of new intracellular delivery systems by membrane destabilizing mechanisms (Wasungu and Hoekstra, 2006).These polymers can be tailored to interact actively with phospholipid membranes upon external stimulation, such as acidification of the surrounding medium. This strategy has been exploited to improve the cytoplasmic delivery of biomolecules (DNA, proteins) that enter cells by endocytosis and end up in acidic organelles (Gupta et al, 2005). 

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