Kinetic-mechanistic studies of lipase-polymer micelle binding and catalytic degradation: Enzyme interfacial activation

Relatively small and uniformly sized block copolymer micelles from low polydispersity poly (ethylene glycol) (PEG) block poly (ε-caprolactone) (PCL) (PEG45-b-PCL60) give 1H NMR spectra useful for direct micelle characterization and kinetic-mechanistic studies. P. cepacia lipase catalyzed PEG45-b-PCL60 micelle degradations were followed by 1H NMR and GPC to obtain simultaneous evaluation of the micelle composition, degradation kinetics and appearance of the water soluble hydrolysis products. Analysis and simulation of the concentration versus time profiles for P. cepacia lipase catalyzed PEG45-b-PCL60 micelle degradation show that the process conforms to a Michaelis-Menten mechanism (E + M⇌EM → P + E) with enzyme-micelle complex product inhibition (EM + P⇌EMP). Formation and tight binding of the lipase enzyme-micelle complex, activation of lipase catalysis and sequential micelle degradation are characteristics of PEG45-b-PCL60 micelle degradation which parallel features of enzyme interfacial activation associated with lipase catalyzed hydrolysis of lipids in membranes.