Using hydrated reversed micelles to evaluate the dimensions of polymer-protein adducts

Hydrolysis of N-trans-cynnamoylimidazole catalyzed by conjugates and comple xes of alpha-chymotrypsin (ChT) with poly(ethylene glycol) (PEG) of differe nt molecular mass (from 300 to 5000 daltons) was studied in the system of t he hydrated reversed micelles of aerosol OT (AOT) in octane at 25 degrees C . The plot of the deacylation constant k(3) for PEG-ChT conjugates and comp lexes versus the degree of hydration of reversed micelles (w(o) = [H2O]/[AO T]) was studied. These plots are hell-shaped with maxima shifted to higher degrees of micelle hydration compared to the corresponding value of the shi ft for ChT. As for PEG-ChT conjugates, the value of the shift of w(o) incre ases with increasing of molecular mass of the attached PEG and/ or with the number of polymer chains per ChT molecule. Another picture was observed fo r PEG-ChT complexes for which the position of the maximum on k(3) versus w( o) curves was practically the same for all compounds. The values of the thi ckness of the polymer layer for PEG-ChT conjugates and complexes were calcu lated. Thus, polymer chains in conjugates placed in hydrated micelles are h ighly packed, whereas in the case of complexes they form a flat layer on th e surface of the protein.