Nomenclature for Modification of Amino Acid Residues

Amino acid residues in proteins may be covalently modified by post-translational modifications. In the case of synthetic peptides , modifications may be inadvertently introduced by side reactions or presence of protecting groups.

To indicate a chemical modification to a specific amino acid, type the residue number followed by the minimal formula of the modification separated by a space. For instance:

256 +C15N5P2O13H19

37 –0.9847

M +O

Non-peptide bonds between two amino acids may be indicated by hyphenating the two residue numbers, without spaces, followed by a space and either (a) a hyphen and the chemical formula of the linker or (b) the word "disulfide". For instance:

37–64 –H2 or 37–64 disulfide

If a protein consists of more than one polypeptide, the residue number must be preceded by the letter that specifies the polypeptide. For instance:

B256 +C15N5P2O13H19

A37 –0.9847

AM +O

A37–B64 disulfide or A37–B64 –H2