Peroxynitrite induces F-actin depolymerization and blockade of myosin ATPase stimulation

Area of Science:

• Biochemistry
• Cell Biology
• Pathophysiology

Background:

• Oxidative stress is implicated in various pathophysiological conditions.
• Actin dynamics are crucial for cellular structure and function.
• The role of peroxynitrite in actin modification requires further elucidation.

Purpose of the Study:

• To investigate the effects of peroxynitrite on F-actin and G-actin.
• To determine the sensitivity of actin polymerization to peroxynitrite.
• To explore the functional consequences of peroxynitrite-induced actin modification.

Main Methods:

• Treatment of purified F-actin with 3-morpholinosydnonimine (SIN-1), a peroxynitrite donor.
• Assessment of F-actin depolymerization and G-actin polymerization kinetics.
• Measurement of cysteine oxidation and myosin ATPase activity.
• Inhibition studies using superoxide dismutase.

Main Results:

• SIN-1 induced a dose-dependent depolymerization of F-actin.
• Peroxynitrite, not decomposed SIN-1, was responsible for F-actin depolymerization.
• F-actin depolymerization was highly sensitive to low peroxynitrite fluxes (50-100nM).
• G-actin polymerization was also impaired by peroxynitrite, albeit with lower sensitivity.
• Submicromolar peroxynitrite fluxes caused cysteine oxidation and blocked actin's stimulation of myosin ATPase activity.

Conclusions:

• Peroxynitrite directly targets F-actin, leading to depolymerization and functional impairment.
• Oxidative stress from peroxynitrite can disrupt the F-actin/G-actin equilibrium.
• These findings suggest a mechanism for myofibril dysfunction in pathophysiological conditions involving peroxynitrite-mediated oxidative stress.