sentences:  The electrophilic centers in the cyclopentenone ring of cylopentenone PGs form covalent bonds with exposed nucleophilic centers, primarily the sulfur atom in the thiol residues of cysteine residues.Proteomics analyses have detected 368 proteins that are covalently modified by 15-deoxy-Δ12,14-PGJ2; these include numerous plasma membrane, cell signaling, glycolytic enzyme, cytoskeletal, and Chaperone (protein)s. This results in the addition of the PG to the protein by a Michael addition reaction and important modifications in the activity of target proteins that have key functions in cells.15-Deoxy-Δ12,14-PGJ2 shows the greatest reactivity and has been the focus of these studies.