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This thesis describes a number of discrete studies in which several novel peptides were discovered within the skin secretion of the African running frog, Kassina senegalens is, by use of reverse phase HPLC fractionation and mass spectrometry. The first of these was a prototype of a new class of antimicrobial hexadecapeptide with myotropic activity, named senegaii n, whose sequence was determined as: FLPFLlPALTSLISSL-amide (Chapter 4). In addition to the known antimicrobial peptides from this species, a novel eicosapeptide, (F lQHLlPLlPHAIQGIKDIF-amide), \vas also isolated and this peptide possessed growth inhibitory activity on cancer cell lines but was only found to be weakly haemolytic (Chapter 7). Two novel amidated peptides were isolated, both of which could induce muscle relaxation: WMSLGWSL-amide (WL-8 amide) (Chapter 5) and CYSAAKYPGFQEFlNRKYKSSRFamide (CF-23-KS) (Chapter 6), respectively. Also of significance. a Kunitz-type chymotrypsin inhibitor was isolated from the skin secretion and this represented the first of its type from an amphibian skin source (Chapter 3). Synthetic chemical replicates of all of these peptides, excepting the Kunitz inhibitor, were prepared in-house by employing solid-phase Fmoc chemistry.

The studies described in this thesis have focused on the bioactive peptides secreted from the skin glands of Rana (Odorrana) frogs, using different techniques to identify the sequences of novel peptides and to subsequently clone their precursors by molecular genetic techniques and finally, to chemically-synthesize these peptides and examine their bioactivities. Chapters I and 2, respectively, give a general introduction to the field of research and describe the scientific techniques employed in the work. The first experimental chapter, Chapter 3, describes two novel non-canonical bradykinin antagonist peptides isolated from the skin secretion of Odorrana versabilis which contain a "Rana box"-like structure at their C-terminals- a motif that is normally present in antimicrobial peptides. Chapter 4 describes a novel tachykinin peptide which was isolated from the skin of Rana chensinensis, and is strongly suspected of being an NKI receptor agonist. Chapter 5 describes the identification of two novel peptides from the skin secretions of Odorrana versabifis and Odorrana livida, which possess a moderate degree of specific antifungal activity. How their similar primary structures with only two residue substitutions, can cause an apparent 4-fold difference in potency is an interesting observation worthy of further indepth study. Chapter 6 describes a study that focuses on a Bowman-Birk trypsin inhibitor peptide from Odorrana schmackeri skin secretion and its position 9 substituted analogue. The most interesting result was the discovery of their multi-functional effects, not only against the proteases, trypsin and chymotrypsin, but also extending to growth inhibitory effects on cancer cell lines, tryptase inhibition and even to smooth muscle effects. The structure/function relationships of these peptides require further in-depth investigations. Chapter 7 describes a novel vasodilator peptide, named vasorelaxin, isolated from Odorrana schmackeri skin secretion with a potency approaching two orders of magnitude greater than canonical bradykinin. These data further illustrate that Rana (Odorrana) frogs skin secretions remain an important resource for novel peptide discovery, some of which may possess therapeutic properties.

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