Dramatic rate enhancements are observed for the oxidation of phenols, including tyrosine, at indium tin oxide electrodes modified by the addition of the electron-transfer relays [M-II(bpy)(2)(4,4'-(HO)(2)P(O)CH2)(2)bpy)](2+) (M = Ru, Os) with clear evidence for the importance of proton-coupled electron transfer and concerted electron proton transfer.