Supramolecular complexes of polyethylene glycol-alpha-chymotrypsin covalent and noncovalent adducts with polyoxyethylene-modified cyclodextrins

Complexes of covalent and noncovalent adducts of polyethylene glycol (PEG) and alpha-chymotrypsin (ChT), PEG-ChT, were generated in the presence of be ta-cyclodextrin derivatives of polyoxyethylene (beta CD-PEO), and their the rmal stability was studied. The covalent [PEG-ChT](c) conjugates were obtai ned by chemical modification of the protein amino groups with the monoaldeh yde derivatives of monomethoxypolyethylene glycol. The non-covalent [PEG-Ch T](n) complexes were obtained by the treatment of ChT-PEG mixtures with inc reasing pressure (1.1-400 MPa). Supramolecular structures resulting from co mplex formation between PEG chains of the PEG-ChT adducts (PEG(ad)) and bet a CD-PEO were studied. The decrease in the rate constant of the slow stage of ChT thermal inactivation in PEG-ChT adducts (k(2)) can serve as confirma tion of complex formation between beta CD-PEO and PEG(ad). The stoichiometr ic composition of our supramolecular structures was determined from the k(2 ) dependence on the molar ratio of beta CD-PEO to PEG(ad). It was shown tha t each polymeric chain in the [PEG-ChT](c) conjugates forms an inclusion co mplex with beta CD-PEO, whereas only half of the PEG(ad) polymeric chains p articipate in the formation of supramolecular structures in the case of [PE G-ChT](n) complexes. Although covalent and noncovalent PEG-ChT adducts of t he same composition significantly differ in their thermal stability, the ma ximal values of the k(2) rate constants for [PEG-ChT](c) and [PEG-ChT](n) a dducts in the triple system attainable at the (beta CD-PEO) to (PEG(ad)) ra tio corresponding to the stoichiometry of the resulting ternary systems are practically the same (k(2) = 0.007 c(-1) at 45 degrees C in 0.02 M Tris-HC l 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.