Amperometric enzyme electrodes: Part III. A conducting salt electrode for the oxidation of four different flavoenzymes

Abstract The conducting organic salt tetrathiafulvalinium tetracyanoquinodimethanide (TTF + TCNQ − ) has been used as an electrode material in a membrane electrode for the direct oxidation of four flavoenzymes: xanthine oxidase, D-amino acid oxidase, L-amino acid oxidase and choline oxidase. For the first three enzymes kinetic analysis shows that under unsaturated conditions the enzyme and electrochemical kinetics are so rapid that the rate limiting step is transport of substrate through the membrane. In the case of choline oxidase the transport and enzyme kinetics were comparable. The saturated behaviour of each enzyme electrode is determined by the direct electrochemical oxidation of the enzyme and values for the electrochemical rate constants are reported.