2011 Volume 28 Issue 4 Pages 308-316
D/L-isomerization of a particular amino-acid residue of bioactive peptides is a rare, but attractive phenomenon. NdWFa (Asn-D-Trp-Phe-NH2) is a D-Trp-containing neuropeptide, originally identified in an opistobranch gastropod, Aplysia kurodai. In this animal, the major source of NdWFa is neurons located in the right-upper quadrant of the abdominal ganglion. NdWFa has a potent cardioexcitatry action on the Aplysia heart with the threshold concentration around 10-10 M. It also induces contraction of blood vessels of the animal. NdWFa has high resistance to digestion by peptidase, although it is inactivated by deamidase activity in nervous tissue of the animal. The nuclear magnetic resonance analysis demonstrated a unique structure of NdWFa, which is not observed when the D-Trp is replaced to L-Trp. This structure seems to be essential for the bioactivity on the Aplysia heart and resistance to peptidase digestion of the peptide. In this review, we will describe the identification, localization, physiological activities and precursor gene of NdWFa to exemplify the D-amino acid containing neuropeptide in gastropods. We will also refer to the D/L-isomerase that converts L-amino acid to D-amino acid in the post-translational modification of bioactive peptides.
