PubMed · 5785662
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C E Metz. 1969. Predicting the minimum activity required for thyroid-uptake studies.. https://pubmed.ncbi.nlm.nih.gov/5785662/
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Here we describe a method for isolating mono- and di-iodine 125 tyramines from a crude tyramine radio-iodination reaction mixture. Tyramine was radio-iodinated according to a modified chloramine-T method. Mono- and diforms were separated from each other, as well as from free 125I and unreacted tyramine, by means of paper electrophoresis or thin-layer chromatography. Both 125I-tyramine derivatives finally obtained were pure and had high specific activities, which averaged 2500 Ci/mmol for mono-125I-tyramine and 5000 Ci/mmol for di-125I-tyramine. Due to their characteristics, these derivatives can be used for labelling various substances indirectly and preparing in vivo and in vitro tracers of high purity and specific activity, when conjugation labelling is required.
We have studied the capacity of different iodinated derivatives of phenylalanine and tyrosine to inhibit the incorporation of [3H]tyrosine into tubulin catalyzed by tubulin:tyrosine ligase. In contrast to thyronine and its iodinated derivatives, iodotyrosines were efficient inhibitors. That they also functioned as substrates of the enzyme was shown by the effective incorporation of [125I]mono- and diiodotyrosine into tubulin. The label was shown to be located at the carboxy terminus. Labeling by this method conserves the polymerization capacity of tubulin in contrast with classical radioiodination methods involving oxidation.
An improved labeling procedure for 15-(p-[123I]iodophenyl)pentadecanoic acid (IPPA) is reported. The exchange labeling yield was greater than 95%. The radiochemical yield is influenced by the presence of sodium. The major advantage of this method is that very high specific activity i.e. upto 190 mCi/mg labeled IPPA can be prepared.