A peptide bond is a linkage between the building blocks of proteins called amino acids (shorter strings of linked amino acids are known as peptides). A peptide bond forms when the carboxylic acid group (R-C[O]OH) of one amino acid reacts with the amine group (R-NH2) of another. The resulting molecule is an amide with a C–N bond (R-C(O)-NH-R).
While drawn as a single bond, the peptide bond has partial double bond character that enforces a well-defined flat structure. The O atom of the amide has a partial negative charge and is a good hydrogen bond acceptor, while the NH is partially positive and a good hydrogen bond donor. Hydrogen bonds between amides are critical to protein folding, as well as to the structure of deoxyribonucleic acid (DNA ).
The synthesis of proteins involves the formation of many peptide bonds. Cleavage of peptide bonds, involved in digestion of proteins and in many regulatory processes, is carried out by enzymes known as proteases. One such protease is subtilisin, the enzyme frequently added to laundry detergent to cleave many protein contaminants. Angiotensin -converting enzyme (ACE) is an enzyme that targets a specific peptide bond, forming a chemical signal that increases blood pressure. Some blood pressure medications act by blocking ACE.
see also Primary Structure; Proteins.