| Summary: | 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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