N-chloroacetyl-[125I]iodotyramine: an alkylating agent with high specific activity |
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Authors: | D Holowka |
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Institution: | Department of Chemistry, Cornell University, Ithaca, New York 14853, USA |
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Abstract: | The preparation of iodinated N-chloroacetyltyramine and its evaluation as a specific sulfhydryl reagent are described. N-Chloroacetyltyramine was synthesized by a carbodiimide-mediated condensation of chloro- or iodoacetic acid and tyramine·HCL, and the crystalline product was iodinated in a reaction with chloramine T to yield either a 3,5-125I]diiodotyramine derivative, or a trace-iodinated product when carrier-free 125I was employed. These iodinated derivatives react specifically with sulfhydryl groups, as judged by their ability to label reduced but not unreduced ribonuclease A and immunoglobulin E. Specific activities of 1 Ci/mmole in 125I or 131I can be readily achieved with both the diiodinated and trace-iodinated (carrier-free) derivatives, and the specific activity of the former can be used directly to quantitate sulfhydryl groups in subnanomolar quantities of protein. N-Chloroacetyl 125I-labeled tyramine prepared by trace iodination with carrier-free 125I is more useful when very high specific activities (100–1000 mCi/μmol) are required. The utility of these reagents is discussed. |
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