COVALENT MODIFICATION OF MUSHROOM TYROSINASE WITH DIFFERENT AMPHIPHICPOLYMERS FOR PHARMACEUTICAL AND BIOCATALYSIS APPLICATIONS

Two different poly(ethylene glycol) derivatives (linear, mol wt 5000 a nd a branched form, mol wt 10000) and a new polymer (polyl-[acryloylmo rfoline], mol wt 5500) were covalently bound to the enzyme tyrosinase. The polymer-protein conjugates were studied with a view to their pote ntial pharmaceutical application and to their use for the bioconversio n of phenolic substrates in organic solvents. V-max and K-m for the do pa-dopaquinone conversion, thermostability, stability toward inactivat ion by dopa oxidation products, half-life in blood circulation, and be havior in organic solvents for the different adducts were investigated . Arrhenius plots for the dopa-dopaquinone conversion were also obtain ed in order to study the effects of temperature on the different enzym e forms. Covalent attachment of the polymers increased enzyme stabilit y in aqueous solution and the solubility in organic solvents. However, organic solvent solubilization brought about loss of enzyme conformat ion as assessed by CD measurements, which is accompanied by a nonrever sible loss of catalytic activity.