Preparation and chromatographic purification of 125I-[Tyr0]-somatostatin-14 for the use in radioimmunoassay and receptor-binding experiments.
[Tyr0]-somatostatin-14 (SST-14) was converted to the corresponding radiolabeled 125I-[Tyr0]-SST-14 derivative by use of the chloramine-T technique. After solid-phase extraction (SPE) of the crude radiopeptide with microfine silica gel and desorption with acetone-water-acetic acid 39:40:1, the label was subjected to size exclusion chromatography (SEC) on Sephadex G-25 fine. Fractions attributable to the target compound were collected and investigated with respect to their specific as well as non-specific binding to a specific anti-somatostatin antibody. All fractions exhibiting an optimum ratio of specific versus non-specific binding were pooled and lyophilized for their further use in both radioimmunoassay (RIA) measurements of somatostatin like immunoreactivity (SLI) and receptor-binding experiments. A specific activity of approx. 1.6 x 10(6) Ci/M was calculated for the radiolabel prepared in this manner. Approximately 85-90% of radioactivity attributable to labeled [Tyr0]-SST species was incorporated into the desired mono-iodinated component. When 125I-[Tyr0]-SST-14 was purified by reversed-phase high performance liquid chromatography (RP-HPLC) using isocratic elution with 0.1 M triethylammonium formate (TEAF) buffer of pH 2.2 in 22% acetonitrile after prior SPE, specific binding decreases to about 80% compared with the value obtained for the radiopeptide subjected to SEC. Nevertheless, RP-HPLC proves as an efficient tool for rapid purity control of 125I-[Tyr0]-somatostatin-14 samples at different storage time intervals.
Department of Neurology, University of Freiburg, Germany.
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Rissler
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Cramer
D000818:Animals; D002700:Chloramines / Q000378:metabolism; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D007457:Iodine Radioisotopes / Q000737:chemistry; D011863:Radioimmunoassay / Q000379:methods*; D017481:Receptors, Somatostatin / Q000378:metabolism*; D012756:Sheep; D013004:Somatostatin / Q000737:chemistry*; D014105:Tosyl Compounds / Q000378:metabolism
D002700:Chloramines; D007457:Iodine Radioisotopes; D017481:Receptors, Somatostatin; D014105:Tosyl Compounds; C016300:chloramine-T; D013004:Somatostatin