Polyethylene glycol derivative-modified cholesterol oxidase soluble and active in benzene.

Cholesterol oxidase from Nocardia sp. was modified with a synthetic copolymer of polyoxyethylene allylmethyldiether (PEG) and maleic acid anhydride (MA anhydride), poly(PEG-MA anhydride). The modified cholesterol oxidase, in which 64% of the amino groups in the protein molecule were coupled to poly(PEG-MA), was soluble in organic solvents and catalyzed the oxidation reaction of cholesterol in benzene to form 4-cholesten-3-one with the enzymic activity of 0.6 mumol/min/mg protein. Using the modified cholesterol oxidase together with polyethylene glycol-modified peroxidase, coupled reactions shown below took place in Cholesterol + O2----4-Cholesten-3-one + H2O2 H2O2 + o-Phenylenediamine----H2O + Oxidized o-Phenylenediamine transparent benzene solution, not in an emulsified system. The oxidation of cholesterol was directly determined in benzene by measuring the absorbance of oxidized o-phenylenediamine at 490 nm.