Six novel tachykinin- and bombesin-related peptides from the skin of the Australian frog Pseudophryne güntheri.

Six novel peptides belonging to the tachykinin and bombesin families were isolated and sequenced from extracts of the skin of the Australian myobatrachid frog Pseudophryne güntheri. One of these peptides (PG-L) was of the bombesin family and may be considered an N-elongation of the litorin/ranatensin molecule, with which it shares an identical spectrum of activity on isolated smooth muscle preparations. The other five peptides were of the tachykinin family with two of these peptides (PG-SPI and PG-SPII) related to substance P and three (PG-KI, PG-KII and PG-KIII) to kassinin. In contrast to the basic nature of substance P, the PG-SP peptides showed a clear acidic character and displayed a more potent and sustained action on isolated smooth muscle preparations and rat blood pressure than did substance P. Two of the three PG-K peptides were more potent than kassinin; PG-KIII was considerably less potent. PG-KI and PG-KII were also present in a deamidated, poorly active, form.