Acyl exchange mechanisms prominently figure in the anabolic and catabolic processes of biosynthesis of several groups of macromolecules. Formation of the amide linkages in proteins (peptide bonds) occurs through an acyl exchange mechanism, and so does the formation of ester linkages in a triglyceride. Formation of the ester linkages in a triglyceride are acyl exchange mechanisms leading to the loss of the hydroxyl portion of the carboxyl group as water (dehydration). Many of the reactions of the thioester acetyl coA involve nucleophilic acyl substitution.