ELECTROCHEMICAL FIXATION OF CARBON-DIOXIDE IN PYRUVIC-ACID TO YIELD MALIC-ACID USING MALIC ENZYME AS AN ELECTROCATALYST

Electrochemical reduction at a glassy carbon electrode of CO2-saturated Tris buffer solutions containing pyruvic acid, malic enzyme, nicotinamide adenine dinucleotide phosphate, ferredoxin-NADP+-reductase, and methyl viologen yielded malic acid as a result of fixation of CO2 in pyruvic acid. The net current efficiency was close to 100% under appropriate electrolysis conditions, and the turnover number for the active site-subunit of malic enzyme amounted to more than 20000 for an electrolysis for 18 h. The electron transfer from the electrode to methyl viologen seems to be the rate-determining step when the concentration of methyl viologen is less than 2 × 10-5 M, but above this concentration the rate-determining step is changed into the CO2-fixation reaction process at the malic enzyme. © 1990.