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Abstract
Musca kinin (Musdo-K; NTVVLGKKQRFHSWG-NH(2)) and N-terminal truncated analogs of 4-14
residues in length were assayed for diuretic and myotropic activity on housefly Malpighian
tubules and hindgut, respectively. The pentapeptide was the minimum sequence required
for biological activity, but it was > 5 orders of magnitude less potent than the intact
peptide. The pharmacological profiles of the different analogs in the two assays were
very similar, suggesting the same receptor is present on both tissues. Potency was
little affected by the deletion of Asn(1), but was reduced > 10-fold after the removal
of Thr(2). Deletion of the next 5 residues had relatively little effect, but after
the second lysyl residue (Lys(8)) was removed potency fell by one to two orders of
magnitude. There was a similar drop in potency after the removal of Arg(10), and at
100 microM the pentapeptide had only 20% of the diuretic activity of the intact peptide.
The importance of Arg(10) was confirmed by comparing dose-response curves for Musdo-K
[6-15] and Acheta kinin-V (AFSHWG-NH(2)) in the diuretic assay; the substitution of
arginine by alanine produced a significant reduction in potency and some loss of activity.