Electrochemical Oxidation of Cholesterol Catalyzed by Cholesterol Oxidase with Use of an Artificial Electron Mediator

Several redox dyes of phenazine and phenothiazine derivatives including 1-methoxy-5-methylphenazinium methosulfate (MPMS), thionin, azure A, and azure C work well as electron acceptors for reduced cholesterol oxidase (EC 1.1.3.6) (ChOx). Kinetic parameters and equilibrium constants of the enzymatic oxidation of cholesterol obtained suggest that the molecular size and/or hydrophobicity of the redox dyes determines their abilities as the electron acceptors. The electrochemical sensitivity to cholesterol in the detection system using ChOx and the above-mentioned redox compounds is determined by the electron acceptability of the redox compounds, and the employment of either MPMS or thionin allows electrochemical determination of cholesterol at a low electrode potential (0 V vs SCE) in the concentration range 0.25−2.5 mmol dm-3, which covers that in normal human blood.