The peptide content of the glandular secretions of Litoria rubella specimens collected from Derby and Lake Argyle (Kimberley region of Western Australia) and from near Darwin in the Northern Territory are all quite different; this suggests that there are different frog populations in these three areas. These different populations may be indicative of either different species or different sub-species of frog. There are two separate families of peptides in the glandular secretion of 'Litoria rubella': ( i ) those corresponding to the tryptophyllin family (tetra- to hepta -peptides all containing the residues Pro and Trp ), and (ii) the rubellidinins ( pentapeptides all containing two Phe residues at positions 3 and 4). To ate, no biological activity has been found for any of these peptides, but it is suspected that the tryptophyllins may be neurotransmitters or neuromodulators.

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.