Ferric nitrosylated myoglobin catalyzes peroxynitrite scavenging

Area of Science:

• Biochemistry
• Molecular Biology
• Cellular Respiration

Background:

• Myoglobin (Mb) functions as an intracellular oxygen reservoir, oxygen transporter, and scavenger of reactive nitrogen and oxygen species.
• Mb plays a crucial role in protecting mitochondrial respiration from oxidative damage.

Purpose of the Study:

• To investigate the inhibitory effect of nitric oxide (NO) on ferric myoglobin (Mb(III))-mediated peroxynitrite detoxification.
• To elucidate the kinetic parameters of NO binding to Mb(III) and the catalytic activity of the Mb(III)-NO complex in peroxynitrite degradation.

Main Methods:

• Kinetic analysis of nitric oxide (NO) binding to ferric myoglobin (Mb(III)) using equilibrium and rate constant measurements.
• Spectrophotometric determination of the rate constants for Mb(III)-catalyzed peroxynitrite detoxification in the presence and absence of NO.

Main Results:

• Nitric oxide (NO) binds to Mb(III) with a dissociation equilibrium constant (K) of (3.8 ± 0.5) × 10⁻⁵ M.
• Mb(III) catalyzes peroxynitrite detoxification with a second-order rate constant (Pk_on) of (1.9 ± 0.2) × 10⁴ M⁻¹s⁻¹.
• In the presence of NO, Mb(III)-mediated peroxynitrite detoxification is partially inhibited, with the Mb(III)-NO complex showing reduced catalytic activity (Pk_on* = (2.8 ± 0.3) × 10³ M⁻¹s⁻¹).

Conclusions:

• Nitric oxide (NO) modulates the protective functions of myoglobin (Mb) by partially inhibiting its peroxynitrite scavenging activity.
• A dynamic balance exists between NO and peroxynitrite, regulated by the relative concentrations of Mb(III) and the Mb(III)-NO complex.
• This interaction highlights a novel mechanism by which NO influences cellular respiration and oxidative stress management.