Interaction of human myeloperoxidase with nitrite

Area of Science:

• Biochemistry
• Spectroscopy
• Cellular Biology

Background:

• Human neutrophil myeloperoxidase (MPO) is a key enzyme in the innate immune system.
• MPO plays a role in the production of reactive oxygen species and hypochlorous acid.
• Understanding MPO's function and regulation is crucial for inflammatory and infectious diseases.

Purpose of the Study:

• To investigate the effect of nitrite on the spin state of human neutrophil myeloperoxidase.
• To characterize spectral changes in MPO upon reaction with nitrite using EPR and optical spectroscopy.
• To explore the potential of EPR spectroscopy for monitoring MPO activity in intact neutrophils.

Main Methods:

• Electron paramagnetic resonance (EPR) spectroscopy was used to analyze the spin state of MPO.
• Optical spectroscopy, including Soret and visible region measurements, was employed to detect spectral shifts.
• Experiments were conducted on purified MPO and intact neutrophils.

Main Results:

• Nitrite addition caused a conversion of MPO from a ferric high-spin to a low-spin state.
• Significant shifts in optical absorption peaks (Soret from 429 to 447 nm; new visible peaks at 573 and 627 nm) were observed.
• EPR spectra showed distinct changes in g-values (from 6.84, 5.02, 1.95 to 2.55, 2.31, 1.82), with minor differences between MPO isoenzymes.
• The reaction was detectable by EPR in intact neutrophils.

Conclusions:

• Nitrite binding induces a significant conformational change in human neutrophil myeloperoxidase, altering its spin state.
• The observed spectral changes provide a sensitive method for detecting MPO-nitrite interactions.
• EPR detection of this reaction in intact neutrophils offers a promising avenue for in vivo monitoring of NO/nitrite production by these cells.