Synthesis and physicochemical properties of protein conjugates with water-soluble poly(alkylene oxides).

Abstract

Conjugates of proteins (bovine serum albumin (BSA) and alpha-chymotrypsin (CHT) with poly(ethylene glycol) and amphiphilic block copolymers of ethylene oxide and propylene oxide (proxanols) were synthesized, using monoaldehyde polymer derivatives as the amino group modifying reagents. Four types of conjugates varying in the placement of hydrophobic block and type of polymer chain distribution were obtained. Methods of purification and characterization of proteins conjugated with proxanols were developed. It was shown that conjugates based on CHT retain high enzymatic activity toward both substrates investigated--N-benzoyl-L-tyrosine and casein-up to high degrees of modification (11 polymer chains per protein molecule). At the same time, CHT--proxanol conjugates were characterized by higher thermostability, the stabilizing effect increasing in parallel with the degree of modification. It was shown that the alteration of sedimentation coefficients of proteins caused by modification was negligible. On the basis of data obtained by the methods of hydrophobic chromatography, sedimentation, and differential scanning calorimetry, conformational models of protein-proxanol conjugates were suggested. It was supposed that conjugates form compact structures in aqueous solutions, which resemble intramolecular micelles, stabilized by hydrophobic interactions between poly(propylene oxide) blocks of proxanols.