THE PREPARATION OF 131I-LABELLED HUMAN GROWTH HORMONE OF HIGH SPECIFIC RADIOACTIVITY

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Abstract
A simple and rapid method is presented for the preparation of I131-labelled human growth hormone of high specific radioactivity (240-300 [mu]C/[mu]g). Low amounts of carrier-free [I131] iodide (2 mc) are allowed to react, without prior treatment with small quantities of protein (5 [mu]g) in a high-yield reaction (approx. 70% transfer of I131 to protein). The degree of chemical substitution is minimized (0.5-1.0 atom of iodine molecule of protein) by the use of carrier-free [I131] iodide. The I131-labelled hormone (up to 300 uC//ig) contains no detectable degradation products and is immunologically identical with the unlabelled hormone. The loss of immunological reactivity at high specific radioactivities or at high levels of chemical substitution with [I131] iodine is demonstrated.