Polyelectrolyte-protein complexes enzyme activity

The existence of soluble protein-polyelectrolyte complexes makes polyelectrolytes potentially important enzyme carriers, in which the enzyme activity could be controlled. For example, the tryptic digestion of hemoglobin with PAA as a carrier was studied by Morawetz [56] in 1955. The trypsin activity was varied by adjusting pH and polymer concentration. It was found that the carrier could even activate the enzyme at low pH, as shown by Fig. 15.22. As shown in Fig. 15.23, the complex of trypsin with KPVS was found to retain activity in a wide pH range by Kokufuta [57]. Based on the study of trypsin-carboxymethyl-cellulose complexes, Larionova et al. [58] concluded that some protein-polyelectrolyte complexes can provide extra thermal stability at the preservation of high biological activity. 

It should be pointed out that the addition of substances, which could improve the biocompatibility of sol-gel processing and the functional characteristics of the silica matrix, is practiced rather widely. Polyethylene glycol) is one of such additives [110— 113]. Enzyme stabilization was favored by formation of polyelectrolyte complexes with polymers. For example, an increase in the lactate oxidase and glycolate oxidase activity and lifetime took place when they were combined with poly(N-vinylimida-zole) and poly(ethyleneimine), respectively, prior to their immobilization [87,114]. To improve the functional efficiency of entrapped horseradish peroxidase, a graft copolymer of polyvinylimidazole and polyvinylpyridine was added [115,116]. As shown in Refs. [117,118], the denaturation of calcium-binding proteins, cod III parvalbumin and oncomodulin, in the course of sol-gel processing could be decreased by complexation with calcium cations. 

Similar assays for measuring protease activity were also reported by Whitten and coworkers [49], These assays utilize polystyrene microspheres that are coated with streptavidin (a biotin-binding protein) and a biotinylated anionic fluorescent conjugated polyelectrolyte or a cationic polyelectrolyte, A biotinylated quencher-labeled peptide serves as a substrate for the enzyme and when mixed with the microspheres, a strong complex similar to the one in the DNA assays described in Section 13,3,1, through the biotin-avidin interaction is created [49], A schematic drawing of the assay is shown in Figure 13,7,... 

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