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UBC Theses and Dissertations

Investigation of an ion transport peptide in desert locust ventral ganglia Bilgen, Tolga


Previous observations have localised an antidiuretic peptide factor to the ventral ganglia (VG) of the desert locust, Schistocerca gregaria. Homogenates of VG increase active ion transport and fluid reabsorption across locust ilea in vitro. There is evidence to suggest that the VG peptide employs cAMP as a second messenger. As it is unstable at high temperatures and at low pH, the VG peptide is probably not Scg-ITP, an ileal transport peptide previously isolated from the corpora cardiaca (CC). Using a short-circuit current (Isc) bioassay, a direct measurement of active CI" transport across locust ilea, further characterization of the VG peptide was conducted. The peptide is unstable below pH 6.0 and loses all activity at pH 4.75. Extreme loss of activity under reducing conditions suggests the VG peptide requires intact disulfide bridges for its biological activity on assay. Reverse-phase cartridges and a high-performance chromatography column did not prove to be useful in purifying the VG peptide, owing to near complete losses of activity. Recovery of activity improved somewhat on anion-exchange cartridges, but results did not suggest useful separation of the peptide. Partial purification (36-fold increase in specific activity) of the VG peptide was accomplished using a combination of gravity-driven and high-performance size exclusion chromatography. These methods also provided an estimation of the peptide's molecular weight as 38 kDa.

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