Hylambatins

Definition
Hylambatin (Hyl), a dodecapeptide isolated from the skin of the African frog, Hylambates maculatus, belongs to the family of tachykinin or physalaemin-like peptides.

Discovery
It was first isolated from the African rhacophorid frog Hylambates maculates by Yasuhara et al., in the year 19801.

Structural Characteristics
Hyl, a novel tachykinin endecapeptide isolated from the skin of the African frog Hylambates maculatus, must be ascribed to the physalaemin subfamily. It differs structurally from all other known tachykinins mainly in having a methionyl methionine residue at the C-terminus, replacing the usual leucine residue at position 2 from the C-terminal tripeptide -Gly-Leu-Met-NH2 which has been a characteristic feature of all members of the tachykinin family2

Mode of Action
Structure-activity relationship of Hyl and its fragments as studied in the guinea-pig ileum.In a study Hyl and its 12 fragments were tested in the guinea-pig ileum preparation for contractile activities. It was found that all fragments except 3 had contractile activities. The C-terminal fragment as short as the octapeptide sequence was at least as active as the parent molecules. The heptapeptide fragment (Hyl6-12) and the hexapeptide fragment (Hyl7-12) were less active and the C-terminal pentapeptide fragment (Hyl8-12) and the N-terminal hexapeptide fragment (Hyl1-6) were much less active. The N-terminal pentapeptide fragment (Hyl1-5) and the N-terminal fragment from which the N-terminal Asp or Asp-Pro residues were removed (Hyl2-6, Hyl3-6), were inactive at doses used3.

Functions
Hyl, a structurally unique tachykinin: effects on insulin and glucagon secretion: Hyl is the first example of a tachykinin which possesses a methionyl methionine residue at the C-terminus. In a study the effect of Hyl on the secretion of glucoregulatory hormones was examined in the rat. Hyl, injected intravenously in graded doses 10 and 30 min before blood collection. It was found that both plasma glucose and plasma insulin significantly increased, whereas the secretion of glucagon was not affected. This profile of action is different from that of kassinin or substances P, further indicating that Hyl, like other neuropeptides, it may have a role in the regulation of carbohydrate metabolism2.

Parallel bioassay of physalaemin and Hyl on smooth muscle preparations and blood pressure: Hyl, a novel tachykinin endecapeptide isolated from the skin of the African frog Hylambates maculatus, must be ascribed to the physalaemin subfamily. It differs structurally from all other known tachykinins. In parallel bioassay on a number of in-vitro and in-vivo test objects, Hyl and physalaemin were nearly indistinguishable from each other, with few moderate quantitative differences4.

References
1. Yasuhara T, Nakajima T, Falconieri Erspamer G, Erspamer V (1981). New tachykinins Glu2,Pro5-kassinin (Hylambates-kassinin) and hylambatin in the skin of the African rhacophorid frog Hylambates maculatus. Biomed Res., 2:613-617
2. Güllner HG, Harris V, Yajima H, Unger RH (1984). Hylambatin, a structurally unique tachykinin: effects on insulin and glucagon secretion. Arch. Int. Pharmacodyn. Ther., 272(2):304-309.
3. Inoue A, Fukuyasu T, Nakata Y, Yajima H, Nomizu M, Inagaki Y, Asano K, Segawa T (1988). Structure-activity relationship of hylambatin and its fragments as studied in the guinea-pig ileum. J. Pharm. Pharmacol., 40(1):72-73.
4. Falconieri Erspamer G, Mazzanti G, Yasuhara T, Nakajima T (1984). Parallel bioassay of physalaemin and hylambatin on smooth muscle preparations and blood pressure. J. Pharm . Pharmacol., 36(4):284-286.

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