The Who, What, When, Where and Why of Chemistry
Chemistry is not a world unto itself. It is woven firmly into the fabric of the rest of the world, and various fields, from literature to archeology, thread their way through the chemist's text.
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.