Enzyme-like kinetics of ferryloxy myoglobin formation in films on electrodes in microemulsions. J. Phys. Chem. B 2005, 109, 24457

Abstract

Covalently linked films of the ferric heme protein myoglobin and poly-l-lysine on pyrolytic graphite electrodes reacted with tert-butylhydroperoxide (tBuOOH) to form ferryloxy protein species according to Michaelis−Menten enzyme kinetics. Rotating disk voltammetry data obtained in microemulsions, micellar solution, and buffers revealed a strong influence of water phase acidity on kinetic parameters. Microemulsion and surfactant type had a much smaller influence on reaction kinetics, possibly because the reaction takes place entirely in a water environment surrounding Mb in the films in all fluids. A large apparent Michaelis kcat in microemulsions with neutral water phases was offset by much weaker binding as shown by larger protein−substrate dissociation constants (Km). Acidic SDS microemulsions and pH 2 buffer provided the most efficient reaction conditions as judged by the ratio kcat/Km. Apparent kinetic constants are most likely governed by acidity-controlled protein conformations and their binding with tBuOOH in the intermediate protein−substrate complex.