Often, D-amino acids are associated with destructive and toxic effects to living organisms. Recently, it became more and more apparent that some living organisms show "sympathy for the devil" by making use of the amino acids' "wrong" enan-tiomers. "Desired" D-amino acid enantiomers, i.e., D-amino acids produced "intentionally" by evolutionary processes, have been identified in plants (and in food), where considerable quantities seem to be omnipresent. Small peptides that use in their architecture at least one amino acid in its D-configuration have been found in vertebrates and invertebrates. In these cases, the amino acid's D-enantiomer can indeed be assumed to be "intentionally" implemented in the molecular construction of these peptides since the peptide looses its biological activity by inversion of the stereogenic center. Interestingly, "wanted" D-Amino acids have also been identified in the form of free amino acids in mammals, where their specific function, however, is less understood.
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