Structure-function studies on red pigment-concentrating hormone; the significance of the terminal residues

The significance of the terminal residues of the red pigment-concentrating hormone (RPCH: Glu-Leu-Asn-Phe-Ser-Pro-Gly-Trp-NH2) for its blanching effect on crustacean chromatophores has been investigated. The chemical synthesis of the following small analogues, starting from the C-terminal amino acid are described: Ac-Trp-NH2, Boc-Gly-Trp-NH2, Ac-Gly-Trp-NH2, Gly-Trp-NH2, Ac-Pro-Gly-Trp-NH2, Glu-Trp-NH2, Glu-Pro-Gly-Trp-NH2, Ac-Pro-Gly and Glu-Pro-Gly-NH2. Assay of the biological activity of the various synthetic compounds in the shrimp Leander adspersus has established that only the C-terminal tryptophan residue is indispensable for the blanching effect of the hormone, although elongation of the chain length improves its potency.