Kassinin

Kassinin is a peptide derived from the Kassina frog. It belongs to tachykinin family of neuropeptides. It is secreted as a defense response, and is involved in neuropeptide signalling.
The amino acid sequence is H-Asp-Val-Pro-Lys-Ser-Asp-Gln-Phe-Val-Gly-Leu-Met-NH2. 
Ion Transportation in Frog Skin.
In frog skin, tachykinins are responsible for ion transportation. Kassinin is one of the tachykinin peptides, which interacts with NK2 receptor to increase short circuit current (SCC), resulting in an ion transportation in frog skin. Another peptide that belongs to tachykinin family is Eledoisin that interacts with NK3 receptor for stimulation of SCC, but can be reduced by either NK1 or NK2 antagonist. Whereas Kassinin can't be reduced by neither of these NK1, NK2 or NK3 antagonists. Kassinin is very effective in increasing short circuit current to its maximum within 10 minutes with increase of 26.13 ± 1.53μΑ/cm2.
There are some requirements that must be accomplished to gain short circuit stimulation. One of them is to have Phe-X-Gly-Leu-Met-NH2 sequence at C-terminal where X could be Val or Ile. The other requirement is to have 2 or 1 proline residue at N-terminal. If only one proline residue is present, then there must be one basic amino acid present in the sequence. For instance kassinin has one proline residue and one basic amino acid (Lys). Another example would be of enterokassinin that does have one proline reside but doesn't have any basic amino acid in the sequence. Thus it doesn't increase SCC and therefore is ineffective in ion transportation. While kassinin plays an effiecient role in ion transportaion in frog skin. 