Electrochemical Characterization and Bioelectrocatalytic H₂O₂ Sensing of Non-Symbiotic Hexa-Coordinated Sugar Beet Hemoglobins

The biological role of non-symbiotic plant hemoglobins (Hbs) is not well understood. It may involve sensing and signaling of reactive nitrogen and oxygen species–a property that can be used in electrochemical sensing. Here, we electrochemically studied two novel non-symbiotic Beta vulgaris Hbs: BvHb1.2 and BvHb2 expressed in E. coli. At pH 7, we observed close potentials of their Fe^2+/3+ hemes, −349 mV for BvHb1.2 and −345/−457 mV vs. Ag/AgCl for the “open” penta-/“closed” hexa-coordinated states of BvHb2. BvHbs bound and bioelectrocatalytically reduced O₂ and H₂O₂ at potentials significantly exceeding their Fe^2+/3+ heme potentials. BvHb2, with the onset of H₂O₂ reduction at 370 mV, enabled O₂-interference-free 10 μM H₂O₂ detection at 0 mV, with a 87 nA μM⁻¹ cm⁻² sensitivity comparable to some peroxidases. The results underpin broad electrochemical applications of BvHbs in the electroanalysis of reactive species and in electrochemical biotransformations.