D-Amino Acids in Sequences of Secreted Peptides of Multicellular Organisms - Google Books

https://books.google.de/books?id=J0jLCxJ7ZEIC&pg=PA57#v=onepage

Life on earth almost exclusively uses laevorotatory or left-handed amino acids (L-enantiomers), rather than D-enantiomers. Nevertheless, with improved analytical methods, D-amino acids have been detected in a variety of peptides of multi-cellular organisms…