Noncovalent adducts of poly(ethylene glycols) with proteins

A new method of preparation of noncovalent complexes between poly(ethylene glycol) (PEG) and proteins (alpha-chymotrypsin (ChT), lysozyme, bovine seru m albumine) under high pressure has been developed. The involvement of poly mer in the complexes was proved using H-3-labeled PEG. The composition of t he complexes (the number of polymer chains per one ChT molecule) depends on the molecular mass of PEG and decreases with the increase in molecular mas s from 300 to 4000, whereas the portion of the protein (wt %) in complexes does not depend on the molecular mass of incorporated PEG and corresponds t o similar to 70 wt %. The kinetic constants for enzymatic hydrolysis of N-b enzoyl-L-tyrosine ethyl ester and azocasein catalyzed by the PEG-ChT comple xes are identical with the corresponding values for the native ChT. Accordi ng to the data obtained by the method of circular dichroism, the enzyme in the complexes fully retains its secondary structure. The steric availabilit y of PEG polymer chains in the complexes was evaluated by their complexatio n with alpha-cyclodextrin (CyD) or polymer derivatives of beta-CyD modified with PEG; (PEG-beta-CyD). In cont;rast to free PEG, only part of PEG polym er chains (similar to 10%) interact with alpha-CyD. Thus, the complexation of PEG with ChT proceeds by means of multipoint interaction with surface gr oups of the protein globule located far from the active site and results in the sufficient decrease in the availability of polymer chains. The complex es between PEG chains in PEG-protein adducts and PEG-beta-CyD may be consid ered as a novel type of dendritic structures.