Homocysteine is
Homocysteine is a non-proteinogenic alpha- amino acid Homologous to cysteine, differing by an additional methylene bridge (-CH2-) Synthesized from methionine.
Amino-acid in Protein- D form
Amino-acid in Protein- L form
Non-protein alpha amino-acid
Seen in Collagen
Methionine and Cysteine details