Enzyme Oxidizer/Electron acceptor Natural/ Artificial electron donor Co-factor Half-cell reaction Reference Laccase O2   Cu O2+4H++4e-→2H2O [226,228,239,263] Bilirubin oxidase O2   Cu O2+4H++4e-→2H2O [229,231-232] Chloroperoxidase H2O2   Heme H2O2+2H++2e-→2H2O [21] Cytochrome c peroxidase H2O2   Heme H2O2+2H++2e-→2H2O [19] Microperoxidase H2O2   Heme H2O2+2H++2e-→2H2O [28,237,264] Horseradish peroxidase H2O2   Heme H2O2+2H++2e-→2H2O [262] Fumarate reductase Fumarate FAD Fe-S Fumarate+2H++2e- → Succinate [264] Alcohol dehydrogenase Formaldehyde Neutral red NAD Formaldehyde+2H++2e- → Methanol [265] Formaldehyde dehydrogenase Formate Neutral red NAD Formate + 2H++2e- → Formaldehyde + H2O [265] Formate dehydrogenase HCO3- Neutral red NAD HCO3-+2H++2e- → Formate [265] Carbonic anhydrase CO2 Neutral red   CO2+H2O → HCO3-+H+ [265] Hydrogenase H+ Methyl viologen Fe-S 2H++2e- → H2 [238]

Table 2: Some of the most studied enzymes for cathodic reduction and their respective reactions.