Voltammetric behaviour of bovine erythrocyte superoxide dismutase

Abstract

The activity of several enzymes, including those involved in N, fmation, photosynthesis and respiration, is linked to electron storage and transport processes [l]. Therefore, electrochemical properties, such as the formal redox potential (E”) and the number of electrons stored in the molecule, are aspects of primary importance in the chemistry of these kinds of proteins. Classical potentiometric, spectrophotometric and coulometric methods and more recent techniques such as cyclic voltammetry and differential pulse polarography [2] can be used in the determination of these parameters. It is well known that, in general, redox proteins do not show a reversible electrochemical response at mercury and solid electrodes [3]. In several cases, surface modification [4] by adsorption of a suitable molecule (promoter) enhances the rate of the electron transfer and the reversibility of the electrochemical process, thus allowing the use of voltammetric or polarographic techniques in the study of the redox behaviour of enzymes. Bovine erythrocyte superoxide dismutase (BESOD) is a metallo-enzyme containing one Cu”-Zn” pair in each of the two subunits of the molecule [5,6]. Copper and zinc are connected by an imidazole bridge of a histidine residue.