The cyclopentenone structures of PGA2, PGA1, PGJ2, Δ12-PGJ2, and 15-d-Δ12,14-PGJ2 possess α,β-unsaturated carbonyl groups (see Carbonyl group#α,β-Unsaturated carbonyl compounds) which serve to establish high levels of chemical reactivity at nearby carbons 9, 11, and/or 13. These carbons are electrophiles that readily form covalent bonds by acting as acceptors in Michael reactions to form covalent bonds with exposed nucleophile sites, particularly thiol residues, in diverse proteins. The reaction inactivates or reduces the activity of various functionally important target proteins and is one mechanism by which cylopentenone PGs influence cell function.