The Structures of New Peptides From the Australian Red Tree Frog 'Litoria rubella'. The Skin Peptide Profile as a Probe for the Study of Evolutionary Trends of Amphibians

Abstract

Seventeen peptides have been isolated and characterized from specimens of the red tree frog 'Litoria rubella', collected from 15 locations throughout Australia. These can be classified into two families of peptides, viz. ( i ) the tryptophyllins L, of which Phe Pro Trp Leu (NH₂), Phe Pro Trp Pro (NH₂) and pGlu Phe Pro Trp Pro (NH₂) are the major constituents, (ii) two types of rubellidins, the first of which is unique to 'Litoria rubella' [e.g. Val Asp Phe Phe Ala (OH)], and the second [e.g. Gly Leu Gly Asp Ile Leu Gly Leu Leu Gly Leu (NH₂)], containing peptides of the caeridin type (like those isolated from Litoria caerulea and Litoria splendida). These peptides show no significant antimicrobial activity. The tryptophyllins are thought to be neuromodulators or neurotransmitters, but the roles of the anionic rubellidin peptides in the amphibian integument are not understood. A comparison of the skin peptide profiles of live specimens of 'Litoria rubella' collected from different locations suggests that there are a number of discrete populations (perhaps different species or subspecies) in ( i ) an area from Kakadu National Park to the Adelaide River in the Northern Territory, (ii) in and around Alice Springs, (iii) in the north of South Australia, and (iv) in several areas of the Kimberley region of Western Australia. In addition, there appear to be evolving populations along the eastern seaboard of Queensland.