Pronounced activity of enzymes through the incorporation into the core of polyion complex micelles made from charged block copolymers

Compartmentalization of enzymes in the nanometric-scaled container, purposing to improve their stability and availability, has recently attracted a strong interest in the field of pharmaceutics. In this study, the enzymatic activity of lysozyme in the core of polyion complex (PIC) micelles, which were formed from egg white lysozyme and poly(ethylene glycol)-poly(alpha,beta -aspartic acid) block copolymer (PEG-P(Asp)), was evaluated using a colorimetric method. Apparent enzymatic activity of lysozyme entrapped in the core of PIC micelles remarkably increased compared to that of free lysozyme, which is mainly attributed to a decrease in the observed Michaelis constant (K-m,K-obs). The reciprocal of the K-m,K-obs values nicely correlated to the corona thickness of PIC micelles, suggesting that the corona layer of PIC micelle may act as the reservoir of the substrate, p-nitrophenyl penta-N-acetyl-beta -chitopentaoside. This result indicates that the enzymatic activity can be controlled by changing the corona thickness of PIC micelles through a variation in the mixing ratio of PEG-P(Asp) to lysozyme. This type of PIC micelle system entrapping enzyme in the core might be useful for the design of diagnostic as well as targetable therapeutic systems of enzyme including antibody-directed enzyme prodrug therapy (ADEPT). (C) 2001 Elsevier Science B.V. All rights reserved.