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Animal venoms are essentially diverse libraries of compounds evolved to have both high affinity and high specificity, making them ideal targets for bioprospecting. Despite advances in antivenom therapy, envenomations remain clinically significant, accounting for numerous human fatalities. The Indian red scorpion (Mesobuthus tamulus) is a serious threat to life in India, but its venom is poorly characterised. This study examines antigenic and proteomic variability of Mesob. tamulus venoms obtained in two geographical regions with distinct biotopes. In addition to highlighting general venomic differences between the two populations, the study identified a peptide of 2947Da that may prove diagnostic between the venom types. As an aid to the future isolation of specific peptides, particularly those initially identified via their DNA sequences, a mass profile of fractionated, commercially available venom was also generated. Scorpion short insectotoxins may have importance as chloride channel blockers and in cancer therapeutics. Only a few such molecules have been isolated and in general, relatively little is known about their properties. Analysis of a Mesob. tamulus telson cDNA library, using probes based upon the signal peptide sequence of a known short insectotoxin (Bm12 from Buthus martensii), yielded two novel "short-insectotoxin" sequences, BtCh11 and BtChl2. Mass spectrometry-guided isolation has been used to purify a corresponding peptide from the venom, based upon its calculated mass. Additional studies using the same cDNA revealed evidence supporting the amidation of tamulustoxin (a potassium channel toxin found in the venom of this species), and evidence to suggest the existence of a novel long-chain potassium channel toxin. Toxins also play an important role as molecular probes for the dissection of ion channel structure. The structure-function relationships of apamin (a calcium-activated potassium channel toxin from the honey bee, Apis mellifera) were examined by investigating the effect of addition of a fluorescent label, non-native disulphide pairings, and disruption of the B-tum on the toxin's affinity for its receptor on rat brain membranes.

Large volumes of antisera were generated against Apis melli/era venom with which to develop a novel, platform technology for the inexpensive production of anti venoms. The ovine sera contained high levels of specific antibodies which neutralised the myotoxic, phospholipase A2 and in vivo activities of the venom. Methods of processing the antisera to provide Fab or F(ab')2 were investigated. F(ab')2 was thought to be clinically advantageous and, by determining the conditions necessary for the preferential breakdown of Fc and serum components other than F(ab')2' it was possible to avoid salt precipitation. Diafiltration was then used to remove most of the unwanted small fragments and anion-exchange chromatography to remove any remaining acidic impurities such as pepsin and large aggregates. The F(ab')2 was -97% pure and the yield - 199 per L of serum. This is the first specific therapy for mass envenoming by European or Africanised bees. Spiders of the genus Latrodectus (black widows) are distributed widely and about 2,500 bites are reported annually in the USA. The neurotoxic effects of the venom were studied on the isolated phrenic nerve diaphragm preparation. Low venom concentrations (ImgIL) were stimulatory while high concentrations (IOmg/L) caused nerve blockade which was potentiated by increased calcium levels. Although effective, the Merck antivenom, which is unprocessed horse serum, causes unacceptable risks. The second purpose of this project was to prepare an improved Latrodectus spider antivenom using the new platform technology. Different immunisation schedules were studied to optimise the humoral immune response. Sheep immunised with 2mg La. hesperus venom produced the highest levels of specific antibodies as assessed by ELISA, using the isolated nerve diaphragm preparation or in vivo in mice. The new process provided a pure F(ab')2 antivenom retaining 78% of the original antisera ED so neutralising power and was - twice as effective as the Merck antivenom.

Previous publications comprise main text of thesis / Includes bibliographical references / 1 v. (various pagings) : / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (M.D.)--University of Adelaide, Dept. of Pathology, 1988