Field of Science

Unnatural Amino Acids

Thirty years ago, it was assumed that all amino acid residues in naturally occurring polypeptides were in the L-form. We now know there are a few exceptions. For example, some polypeptide antibiotics found in fungi incorporate D-amino acids. It is thought that in most cases the peptide is synthesized with all L-amino acids, subsequently individual amino acids undergo enzymatically catalyzed epimerization. Only one such epimerase has been identified to date. The serine epimerase found in the venom of the funnel web spider, Agelenopsis aperta, selectively inverts the configuration of Ser-46 of the substrate omega-agatoxin-TK, leaving the other serine residue at position 28 untouched.


  1. One of the amazing things I remember learning in introductory organic was how that all molecules used by life forms are stereo-specific.

    1. Thanks for your comment, Tim!
      It was by far the coolest story that I have heard today!
      I would love for you to tell it again!!!

  2. More and more peptides contained unnatural amino acids found in natural products mainly secondary metabolites. They are very unique and biosynthesized by non ribosomal peptide synthase


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