Protein Nitration

Functionally, protein tyrosine nitration lowers the pKa of tyrosine, increases hydrophobicity, and can induce structural and steric changes. In plants, nitration generally leads to loss of protein function. For instance, peroxynitrite-associated nitration targets Tyr348 and Tyr360 in pepper catalase inducing its down-regulation which favours for hydrogen peroxide accumulation during ripening (González-Gordo et al., 2024). A further example from pepper is the H₂S-generating cytosolic L-cysteine desulfhydrase, which was reported to be nitrated at Tyr82 and Tyr254, resulting in loss of enzymatic activity in pepper fruits (Muñoz-Vargas et al., 2023). In animals, nitration can either activate, inactivate, or have no effect on protein activity, and functional changes are not always directly caused by tyrosine modification alone.

Tyrosine nitration can also positively or negatively affect tyrosine phosphorylation, thereby influencing cell signaling. While this relationship is well documented in non-plant systems, evidence in plants remains limited. Nonetheless, disruptions in microtubule organization and protein stability suggest a functional interplay between tyrosine nitration and phosphorylation, potentially through competition for the same tyrosine residues (Kolbert et al., 2017).