Revisiting the nitrite reductase activity of hemoglobin with differential pulse voltammetry

Area of Science:

• Biochemistry
• Electrochemistry
• Physiology

Background:

• Nitric oxide (NO) is a vital signaling molecule in vertebrates, regulating blood flow and neural activity.
• The nitrite anion is a key precursor for nitric oxide (NO) generation.
• Hemoglobin facilitates nitrite reduction to NO within the vascular system.

Purpose of the Study:

• To investigate and characterize the nitrite reductase activity (NRA) of hemoglobin using electrochemical methods.
• To explore the distinct electrochemical reduction pathways of nitrite by hemoglobin in different oxidation states.
• To establish a foundation for understanding hemoglobin's direct electrochemistry.

Main Methods:

• Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were employed to study NRA.
• Electrochemical analysis was conducted over a broad potential window (+0.3 V to -1.3 V vs. Ag/AgCl).
• Hemoglobin and hemoglobin-S NRA were compared in a didodecyldimethyl ammonium bromide (DDAB) liquid crystal film.

Main Results:

• Two distinct reduction regimes for nitrite by hemoglobin were identified, corresponding to Fe(II) and Fe(I) states.
• Both reactions exhibited reversible behavior within the experimental timescale.
• The Fe(II) state showed normal redox behavior, while the Fe(I) state displayed catalytic electro-reduction/oxidation characteristics.

Conclusions:

• This research provides the first detailed electrochemical characterization of hemoglobin's nitrite reductase activity.
• The findings elucidate the mechanisms of nitrite reduction by hemoglobin, highlighting different redox behaviors.
• The study offers a simplified, mediator-free platform for investigating hemoglobin electrochemistry and NRA.