Synthesis of the red-pigment-concentrating hormone of the shrimp, Pandalus borealis

Amino acid sequences of neuropeptides in the sinus gland of the land crab Cardisoma carnifex: a novel neuropeptide proteolysis site

The sinus gland is a major neurosecretory structure in Crustacea. Five peptides, labeled C, D, E, F, and I, isolated from the sinus gland of the land crab have been hypothesized to arise from the incomplete proteolysis at two internal sites on a single biosynthetic intermediate peptide "H", based on amino acid composition additivities and pulse-chase radiolabeling studies. The presence of only a single major precursor for the sinus gland peptides implies that peptide H may be synthesized on a common precursor with crustacean hyperglycemic hormone forms, "J" and "L," and a peptide, "K," similar to peptides with molt inhibiting activity. Here I report amino acid sequences of these peptides. The amino terminal sequence of the parent peptide, H, (and the homologous fragments) proved refractory to Edman degradation. Data from amino acid analysis and carboxypeptidase digestion of the naturally occurring fragments and of fragments produced by endopeptidase digestion were used together with Edman degradation to obtain the sequences. Amino acid analysis of fragments of the naturally occurring "overlap" peptides (those produced by internal cleavage at one site on H) was used to obtain the sequences across the cleavage sites. The amino acid sequence of the land crab peptide H is Arg-Ser-Ala-Asp-Gly-Phe-Gly-Arg-Met-Glu-Ser-Leu-Leu-Thr-Ser-Leu-Arg-Gly- Ser-Ala-Glu- Ser-Pro-Ala-Ala-Leu-Gly-Glu-Ala-Ser-Ala-Ala-His-Pro-Leu-Glu. In vivo cleavage at one site involves excision of arginine from the sequence Leu-Arg-Gly, whereas cleavage at the other site involves excision of serine from the sequence Glu-Ser-Leu. Proteolysis at the latter sequence has not been previously reported in intact secretory granules. The aspartate at position 4 is possibly covalently modified.

Structure-activity relationships for the lipid-mobilising action of locust adipokinetic hormone. Synthesis and activity of a series of hormone analogues

A series of compounds structurally related to adipokinetic hormone, the decapeptide neurohormone less than Glu-Leu-Asn-Phe-Thr-Pro-Asn-Trp-Gly-Thr-NH2, have been prepared by synthesis and by enzymic cleavages of synthetic hormone. Their relative agonist activities in mobilising lipids over a fixed time interval (1 h) in locusts were assessed. The similar time courses for lipid release shown by two of the peptide analogues and adipokinetic hormone suggest that the analogues and the hormone are transported to the receptors on the fat body cells, and are also degraded, at similar rates. Consequently, the analogue activities can be correlated with the structural requirements of the locust fat body hormone receptors. The requirements for activity demonstrated in this study are as follows. Residues 1--8 from the N-terminus are necessary to elicit some activity (20%). Residues 5 and 7 in the octapeptide can be changed without affecting activity but L-pyroglutamic acid as the N-terminal residue is necessary formaximum activity both in the octapeptide and the decapeptide. Full activity is achieved only by adding the dipeptide glycyl threonine amide to the active octapeptide 'core'. In the decapeptide, residues cannot be interchanged to the same extent as in the octapeptide without reducing activity. The peptide probably has to be uncharged. Inactive analogues of seven residues or less do not interfere in the hormone-receptor interaction.