An activity in rat tissues that modifies nitrotyrosine-containing proteins

Area of Science:

• Biochemistry
• Molecular Biology
• Toxicology

Background:

• Protein nitration, indicated by nitrotyrosine, is linked to oxidative stress and cellular damage.
• Understanding mechanisms that reverse protein nitration is crucial for mitigating associated toxicity.

Purpose of the Study:

• To identify and characterize enzymatic activity capable of removing nitrotyrosine epitopes from proteins.
• To investigate the potential role of this activity in reducing peroxynitrite-induced toxicity.

Main Methods:

• Incubation of nitrotyrosine-containing bovine serum albumin (BSA) with rat spleen and lung homogenates.
• Assessing loss of nitrotyrosine epitope using monoclonal antibody detection.
• Employing protease inhibitors to distinguish epitope loss from protein degradation.
• Fractionation of homogenates and characterization of the active factor's properties (heat lability, trypsin sensitivity, molecular weight cutoff).

Main Results:

• Spleen and lung homogenates removed nitrotyrosine epitopes from BSA without causing protein degradation.
• The activity was heat labile, trypsin sensitive, and associated with a soluble factor <10 kDa.
• Activity was inducible by endotoxin (bacterial lipopolysaccharide) treatment and showed time- and concentration dependence.
• The activity was specific for certain nitrotyrosine-containing proteins and not observed in liver or kidney homogenates.

Conclusions:

• A novel, inducible enzymatic activity, potentially a "nitrotyrosine denitrase," exists in rat spleen and lung.
• This enzyme reverses protein nitration, suggesting a protective role against peroxynitrite toxicity.
• The tissue-specific nature of this activity warrants further investigation into its physiological relevance.