Oxidation of deoxyhemerythrin to semi-methemerythrin by nitrite

Area of Science:

• Biochemistry
• Bioinorganic Chemistry
• Spectroscopy

Background:

• Deoxyhemerythrin is an iron-containing protein involved in oxygen transport.
• Oxidation of hemerythrin can lead to various states, including methemerythrin.
• Understanding the oxidation mechanisms is crucial for elucidating protein function.

Purpose of the Study:

• To investigate the oxidation mechanism of deoxyhemerythrin by sodium nitrite.
• To characterize the intermediate species and final products of the oxidation.
• To determine the role of nitrous acid and nitrite in the reaction.

Main Methods:

• Anaerobic phosphate buffer experiments at controlled pH.
• Spectroscopic analysis, including EPR spectroscopy.
• Monitoring absorbance changes over time to determine reaction kinetics.

Main Results:

• Deoxyhemerythrin is quantitatively oxidized to semi-methemerythrin by excess sodium nitrite.
• The oxidation proceeds in two phases, with the first phase dependent on H+ and NO2- concentrations.
• Nitrous acid is identified as the initial oxidant, forming a nitrosyl adduct, followed by a slower nitrite adduct formation.

Conclusions:

• Nitrite is a unique oxidant of deoxyhemerythrin, yielding semi-methemerythrin as the stable product.
• The oxidation mechanism involves an 'inner-sphere' process initiated by nitrous acid.
• The formation of stable adducts with the oxidant or its products stabilizes the semi-methemerythrin state.