As mentioned previously, the EA for electron transfer in cytochrome c is approximately 15 kJ mol -1 , 56,57 whereas the activation barriers for bioelectrocatalytic reactions, or for (bio)chemical reactions in general, are typically equal to or higher than 40 kJ mol -1 . Therefore, observations of EA eff that are lower than 20 kJ mol -1 are evidence of strong limitations to electron transport, whereas values approaching 40 kJ mol -1 indicate an onset of limitations to the enzymatic oxidation of acetate.