[Supramolecular complexes of polyethylene glycol-alpha-Chymotrypsin covalent and noncovalent adducts with...

Complexes of covalent and noncovalent adducts of polyethylene glycol (PEG) and alpha-chymotrypsin (ChT), PEG-ChT, were generated in the presence of beta-cyclodextrin derivatives of polyoxyethylene (beta CD-PEO), and their thermal stability was studied. The covalent [PEG-ChT]c conjugates were obtained by chemical modification of the protein amino groups with the monoaldehyde derivatives of monomethoxypolyethylene glycol. The noncovalent [PEG-ChT]n complexes were obtained by the treatment of ChT-PEG mixtures with increasing pressure (1.1-400 MPa). Supramolecular structures resulting from complex formation between PEG chains of the PEG-ChT adducts (PEGad) and beta CD-PEO were studied. The decrease in the rate constant of the slow stage of ChT thermal inactivation in PEG-ChT adducts (k2) can serve as confirmation of complex formation between beta CD-PEO and PEGad. The stoichiometric composition of our supramolecular structures was determined from the k2 dependence on the molar ratio of beta CD-PEO to PEGad. It was shown that each polymeric chain in the [PEG-ChT]c conjugates forms an inclusion complex with beta CD-PEO, whereas only half of the PEGad polymeric chains participate in the formation of supramolecular structures in the case of [PEG-ChT]n complexes. Although covalent and noncovalent PEG-ChT adducts of the same composition significantly differ in their thermal stability, the maximal values of the k2 rate constants for [PEG-ChT]c and [PEG-ChT]n adducts in the triple system attainable at the (beta CD-PEO) to (PEGad) ratio corresponding to the stoichiometry of the resulting ternary systems are practically the same (k2 = 0.007 c-1 at 45 degrees C in 0.02 M Tris-HCl buffer solution, pH 8.0). Structures for the supramolecular dendrite-like ensembles formed upon the interaction of covalent and noncovalent PEG-ChT adducts with beta CD-PEO were suggested.