The [mechanism](href="") of action of PPIs involves the interconversion between the cis and trans forms of peptide bonds. This process is often slow and can be a rate-limiting step in protein folding. PPIs accelerate this isomerization by stabilizing the transition state, thus lowering the activation energy required for the reaction. The enzyme binds to the substrate, typically a peptide or protein, and facilitates the rotation around the prolyl bond.
