SPECTROPHOTOMETRIC AND ELECTROCHEMICAL KINETIC-STUDIES OF POLY(ETHYLENE GLYCOL)-MODIFIED HORSERADISH-PEROXIDASE REACTIONS IN ORGANIC-SOLVENTS AND AQUEOUS BUFFERS

The dynamics of the horseradish peroxidase-catalyzed oxidation of catechol and ferrocene derivative reductants by the oxidants tert-butyl hydroperoxide and hydrogen peroxide at saturating concentrations have been studied in aqueous buffers and in the organic solvents ethyl acetate and 1,2-dichlorobenzene. The enzyme, modified with poly(ethylene glycol) (PEG) so as to be soluble in both aqueous and organic solvents, catalyzes the same reactions in organic and aqueous solutions but more slowly in organic solutions. Comparisons between spectrophotometric and electrochemical kinetic procedures confirm the methodology. The enzyme-reductant reaction rates are first order in reductant and in enzyme at low turnover rates in the organic media, but level off at high turnover rates. Influences on reaction rates of reductant redox potential, steric built, hydrophobicity, and charge, and of buffer, electrolyte, and pH are also discussed.