The anurans (frogs and toads) granular glands are a rich source of biologically active compounds, including biogenic amines, steroids, bufadienolides and proteins and peptides. The release in skin secretions of peptides with antibacterial and antifungal properties is a feature of several species of anurans. These antimicrobial peptides are 10-46 amino acid residues long and usually synthesized as members of structurally-related families. They are probably involved in the protection of the animal against invasion by pathogenic microorganisms. With very few exceptions, the anurans antimicrobial peptides are cationic, relatively hydrophobic and have the propensity to form an amphipathic α-helix in a membrane-mimetic solvent.

               One unique antimicrobial peptide was isolated from electrically stimulated skin secretion of the Brazilian pepper-frog Leptodactylus labyrinthicus. Aliquots (12-17 mg) of crude skin secretion were dissolved in 200 mL of 0.1% (v/v) TFA/water and fractioned on a C₁₈ semi-preparative HPLC column (Vydac 218TP1010). All fractions were manually collected and freeze‑dried. Antimicrobial activity was monitored against Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 25923) using susceptibility microdilution assays. One active fraction against E. coli was analyzed by MALDI-TOF (Reflex IV, Bruker) mass spectrometry and exhibits a molecular mass of 1,762.4 [M+H]⁺. The primary structure of this peptide was determined by Edman degradation revealing a sequence very rich in glycine and leucine residues (95% of the total). This peptide displays low identity (~30%) to other antimicrobial peptides already isolated from frogs of the same genus and species (L. ocellatus, L. labyrinthicus, L. fallax and L. pentadactylus), although it exhibits high identity (≥50%) to antimicrobial peptides from anurans of the families Bombinatoridae, Hylidae and Pipidae.

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