The dorsal glandular extract of the toadlet Uperoleia mjobergii contains more than 20 peptides. We report the amino acid sequences of the seven major peptides: these were determined by a combination of mass spectrometry and automated Edman sequencing. Three of these peptides have 19 amino acid residues and belong to the uperin 2 group of peptides [e.g. uperin 2.6, Gly Ile Leu Asp Ile Ala Lys Lys Leu Val Gly Gly Ile Arg Asn Val Leu Gly Ile (OH)], while the other four have 17 residues and are classified as uperins 3 [e.g. Uperin 3.4, Gly Val Gly Asp Leu Ile Arg Lys Ala Val Ala Ala Ile Lys Asn Ile Val (NH2)]. Several of these cationic peptides have been synthesized in order for bioassays to be carried out: they show significant antibiotic activity against a range of Gram-positive microorganisms. A major skin peptide from the related species Uperoleia inundata is a powerful neuropeptide named uperin 1.1 ([Ala2] uperolein ): no corresponding neuropeptide is detected in the skin glands of Uperoleia mjobergii.

The dorsal glandular extract of the floodplain toadlet Uperoleia inundata contains more than 50 peptides: we report the amino acid sequences and bioactivity data of 13 of these. The peptides have been sequenced by using a combination of mass spectrometry and automated Edman sequencing. Ten of the peptides have been synthesized in order to confirm their structures, and to enable bioassays to be carried out. Ten peptides are host- defence agents, including ( i ) a powerful new neuropeptide of the tachykinin family which we name uperin 1.1 [ pGlu Ala Asp Pro Asn Ala Phe Tyr Gly Leu Met (NH2)], and (ii) nine antibiotic peptides including five uperins 2 [e.g. uperin 2.1, Gly Ile Val Asp Phe Ala Lys Lys Val Val Gly Gly Ile Arg Asn Ala Leu Gly Ile (OH)], three uperins 3 [e.g. uperin 3.1, Gly Val Leu Asp Ala Phe Arg Lys Ile Ala Thr Val Val Lys Asn Val Val (NH2)] and uperin 4.1 [ Gly Val Gly Ser Phe Ile His Lys Val Val Ser Ala Ile Lys Asn Val Ala (NH2)]. The function of the three other characterized peptides in the amphibian integument is not known, viz. ( i ) uperin 5.1 [ Phe Gln Phe Val Asn Pro Ser Asp Ile Val Phe Gly Ser (OH)] and (ii) the two uperins 6 [e.g. uperin 6.1, Gly Leu Ala Gly Ala Ile Ser Ser Ala Leu Asp Lys Leu Lys Gln Ser Gln Leu Ile Lys Asn Tyr Ala Lys Lys Leu Gly Tyr Pro Arg (OH)].

The collision-induced mass spectra (MS/MS) of (M - H)- ions derived from dipeptide methyl esters containing serine or threonine lack the characteristic backbone cleavage of the underivatized peptides (which provide primary sequencing data). Instead, competitive fragmentation occurs through the ester and α-side chain functions. For example, Ser methyl esters lose both CH2O (from the side chain) and MeOH ( MeO comes from the methyl ester). Isomeric dipeptides may be differentiated by competitive fragmentations; for example [ Gly Ser( OMe )-H]- fragments first by loss of CH2O, while [Ser Gly ( OMe )-H]-, in contrast, shows initial elimination of MeOH. The structures of the product ions in these spectra have been probed by deuterium labelling and MS/MS/MS studies.

The dermal glandular extracts of the tibial (calf) glands of the Australian banjo frogs Limnodynastes interioris, Limnodynastes dumerilii and Limnodynastes terraereginae each contain a different peptide, which we have named dynastin 1, 2 and 3 respectively. The determination of the sequences of these peptides is detailed.

The dermal glandular extracts of the Australian frog Limnodynastes salmini contain a number of peptides of the dynastin family. The related species Limnodynastes fletcheri contains only one peptide in its glandular extract; this compound, which we have named fletcherin, is unusual amongst amphibian peptides in that the N-terminal group corresponds to Ala. The primary structures of the dynastins and fletcherin are described.