Tyrosine modification by reactive nitrogen species: a closer look

Area of Science:

• Biochemistry
• Oxidative Stress
• Reactive Nitrogen Species

Background:

• Peroxynitrite (ONOO-) is a potent oxidant formed from nitric oxide (.NO) and superoxide (O2.-).
• Protonated peroxynitrite (ONOOH) decomposes into reactive intermediates similar to hydroxyl (.OH) and nitrogen dioxide (.NO2) radicals.
• Tyrosine modification by peroxynitrite involves aromatic nitration, potentially via radical mechanisms.

Purpose of the Study:

• Investigate tyrosine modification mechanisms by peroxynitrite and related reactive nitrogen species.
• Elucidate the roles of tyrosyl radicals and .NO2 in tyrosine nitration.
• Determine the pH dependence and reaction kinetics of tyrosine modification.

Main Methods:

• Reaction of tyrosine with peroxynitrite (ONOO-), 3-morpholinosydnonimine (SIN-1), and .NO2.
• Generation of peroxynitrite using H2O2 and NaNO2 at acidic pH.
• Utilized hydroxyl radical scavengers to probe reaction mechanisms.
• Analyzed products including 3-nitrotyrosine and dityrosine.

Main Results:

• Peroxynitrite-induced tyrosine modification yields 3-nitrotyrosine and dityrosine, indicating tyrosyl radical intermediates.
• Formation of these products is pH-dependent, suggesting the requirement of ONOOH.
• Hydroxyl radical scavengers enhanced tyrosine nitration when peroxynitrite was generated slowly, supporting a .NO2-mediated pathway.
• Direct nitration by .NO2 was unaffected by hydroxyl radical scavengers.

Conclusions:

• Peroxynitrite and related systems induce tyrosine nitration through intermediate tyrosyl radicals and .NO2.
• The mechanism involves the decomposition of peroxynitrite and its protonated form, ONOOH.
• Understanding these pathways is crucial for studying oxidative and nitrosative stress in biological systems.