(SGP-T) for Receptor Identification.
JS Davison (Dept of Physiology and Biophysics, University of Calgary, Canada)
R Mathison (Dept of Physiology and Biophysics, University of Calgary, Canada)
SGP-T is a novel heptapeptide isolated from the salivary glands of rat which ameliorates anaphylactic responses both in vivo and in vitro. Labeling the ligands facilitates receptor characterization and isolation, but SGP-T (Thr-Asp-Ile-Phe-Glu-Gly-Gly) lacks any endogenous labeling sites. A series of analogues were developed containing lysine and tyrosine residues and were screened for biological activity using an organ bath containing suspended sections of terminal ileum isolated from ovalbumin-sensitized rats. SGP-T significantly decreased the contraction induced by ovalbumin when administered at a dose of 6.79x10-7M (34.18% ± 7.86% of control), while analogues containing tyrosine were biologically inactive. In contrast, KT (Lys-Gly-Gly-Gly-Gly-Gly-Gly-Thr-Asp-Ile-Phe-Glu-Gly-Gly) significantly decreased antigen induced contractility at doses of 1.03x10-7M (39.95% ± 9.80%), 2.95x10-7M (32.51% ± 7.05%), and 1.03x10-6M (15.86% ± 2.77%). Addition of N-hydroxysuccinimide to the lysine for use as an iodination site destroyed the activity of KT, whereas biotinylation of KT had no adverse effect. Hence, of the analogues developed, only Biotinyl-KT appears to be amenable for use as an agonist. The presence of the biotin group(s) on the N-terminus and/or e-amino offers a powerful tool for further study of SGP-T's receptor.
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