Catalytic Properties of Galactose Oxidase to Liposome-Forming Amphiphiles Which Have Many Pendent Galactose Residues

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Abstract
A galactose-carrying vinyl monomer [2-(methacryloyloxy)ethyl β-d-galactopyranoside, MEGal] was polymerized by using a lipophilic radical initiator. The amphiphiles obtained (DODA-PMEGal) formed stable liposomes by mixing with phospholipids, and the galactose residues on the liposome surface were effectively recognized and oxidized by galactose oxidase. The affinity (estimated by the 1/Km value) of galactose oxidase for the galactose residues on the liposomes was higher than those for free galactose and MEGal and dependent on the length of galactose-carrying polymer chains on the liposome surface and the fluidity of the membranes, whereas not significantly influenced by the surface density of galactose residues on the liposomes. The affinity of galactose oxidase for the galactose-carrying linear polymers, which were prepared by using an ordinary azo-type radical initiator and a chain-transfer reagent, was also higher than those for free galactose and MEGal and dependent on the degree of polymerization of MEGal. The affinity was, however, relatively much smaller than those for DODA-PMEGals incorporated in liposomes.