Improvement of proteolytic resistance of immunoadsorbents by chemical modification with polyethylene glycol

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Abstract
Immunoadsorbents were modified with monomethoxy‐polyethylene glycol (PEG; average molecular weights of 5000 (PEG‐5000) and 1900 (PEG‐1900)) activated with cyanuric acid (activated PEG) by four different methods. In the two methods, anti‐BSA antibodies were modified with activated PEG with and without protection of antigen binding sites with BSA and then were coupled to CNBr‐activated Sepharose 4B. In the other two methods, Immunoadsorbents, which were prepared by coupling anti‐BSA antibodies to CNBr‐activated Sepharose 4B, were modified with activated PEG with and without the protection. The effects of PEG modification by these four methods on the binding ratio (the ratio of the numbers of moles of antigen adsorbed to the numbers of moles of binding sites of antibody coupled), the antigen binding property and the resistance to proteolytic digestion of immunoadsorbents were studied. The decrease in the binding ratio by the modification with activated PEG was small enough to use modified immunoadsorbents for industrial purification processes. The resistance to proteolytic digestion of immunoadsorbents was improved by modification with activated PEG. The modification without protection of antigen binding sites gave higher resistance to proteolytic digestion than that with protection, while the former caused larger decrease in the binding ratio of modification. The immunoadsorbents modified with activated PEG‐5000 showed higher resistance to proteolytic digestion than those modified with activated PEG‐1900.