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Three tritiated analogs of human beta-endorphin have been prepared from their corresponding iodinated analogs. The iodinated analogs (diiodotyrosine at positions 1, 27 or 1 and 27) were synthesized by the solid-phase method and were found to have biological and physical properties which were altered when compared with the native molecule. Catalytic exchange of these iodinated analogs in the presence of tritium yielded tritiated human beta-endorphins having full biological activity and specific activity of 50-100 Ci/mmol. Both the iodinated and tritiated beta-endorphin analogs were shown to be homogeneous by chromatography on carboxymethylcellulose, partition chromatography, paper chromatography, amino acid analysis, electrophoresis, high performance liquid chromatography, and isoelectric focusing on polyacrylamide.
Houghten et al. (Wed,) studied this question.