Abstract
This study deals with the effect of deamidation and C-terminal truncation on the potency of an octadecapeptide pigment-dispersing hormone (PDH: Asn- Ser-Gly-Met-Ile-Asn-Ser-Ile-Leu-Gly-Ile-Pro-Arg-Val-Met-Thr-Glu-Ala-NH 2), first described as light-adapting distal retinal pigment hormone (DRPH) from Pandalus borealis. Bioassay of synthetic analogs for melanophore pigment dispersion in destalked fiddler crabs ( Uca pugilator) showed that deamidation causes a 300-fold decrease in potency. The analogs 1–17-NH 2 and 1–16-NH 2 were about 3 times more potent than 1–18-OH. Further truncation led to decreases in potency, with the peptide 1–9-NH 2 being the smallest C-terminal deletion analog to display activity (0.001% potency). Smaller analogs (1–8-NH 2, 1–6-NH 2 and 1–4-NH 2) were inactive when tested in doses as high as 500 nmoles/crab. On the basis of our earlier work on N-terminal deletion analogs and the present findings the residues 6 to 9 seem to be important for PDH action.
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