Tryptophyllins　are　a　heterogenous　group　of　amphibian　skin　peptides　originally　identified　in　skin　extracts　of　Neotropical　leaf　frogs,　Phyllomedusa　sp.,　by　chemical　means.　Until　now,　biosynthetic　precursor　structure　and　biological　activity　remain　unreported.　Here　we　describe　the　isolation　of　a　novel,　post-translationally　modified　tryptophyllin,　Lys-Pro-Hyp-Ala-Trp-Val-Pro.　amide　(PdT-1),　from　the　skin　secretion　of　the　Mexican　leaf　frog,　Pachymedusa　dacnicolor.　Using　a　3′-　and　5′-RACE　strategy　and　an　in　vitro　skin　cDNA　library,　the　PdT-1-encoding　precursor　was　cloned　and　found　to　consist　of　an　open-reading　frame　of　62　amino　acids　with　a　single　copy　of　PdT-1　located　towards　the　C-terminus.　A　synthetic　replicate　of　PdT-1　was　found　to　be　a　potent　myoactive　agent,　relaxing　mammalian　arterial　smooth　muscle　and　contracting　small　intestinal　smooth　muscle　at　nanomolar　concentrations.　PdT-1　is　thus　the　first　amphibian　skin　tryptophyllin　to　be　pharmacologically　characterized　and　the　first　whose　precursor　cDNA　has　been　cloned.　©　2003　Elsevier　B.V.　All　rights　reserved.