Electrocatalytic oxidation of L-lactate by Saccharomyces cerevisiae flavocytochrome b2 on redox mediator-modified glassy carbon electrodes

In order to expand the variety of redox mediator-modified electrodes potentially used for the determination of L-lactate, in this work we investigated the reactions of Saccharomyces cerevisiae flavocytochrome b2 (fcb2) with quinones and its electrocatalytic reactions on glassy carbon electrodes, modified either by their electrochemical pretreatment, or by the products of the electrochemical reduction of dinitrobenzenes. The obtained electrochemically reversible surface redox groups were characterised by a midpoint potential of 0.06–0.10 V (vs Ag/AgCl, pH 7.0) and an electron transfer rate constant of 0.62–0.72 s–1. In the presence of surface-entrapped fcb2, the electrocatalytic oxidation of L-lactate started atca. 0.10 V, and was characterised by a current density of 4.5–18 µA/cm2 at 0.20 V. The linear part of the response was observed up to 0.3–0.4 mM L-lactate. However, the prepared electrodes were less stable than those using fcb2 of other origin, most likely due to the modification of specific cysteine groups in the enzyme active center.