“Nonstandard” Amino Acids
AA Derivatives in Proteins
- Result from specific modification of an AA residue after polypeptide chain synthesis.
- Some prominent modifications:
- 4-hydroxyproline & 5-hydroxylysine: collagen
- Histones and ribosomal proteins are: methylated, acetylated, phosphorylated.
- N-formylmethionine: N-terminal residue of all prokaryotic proteins
- ?-carboxyglutamic acid: constituent of blood clot proteins