FC Greenwood

A simple and rapid method is presented for the preparation of I/sup 131/- labeled human growth hormone of high specific radioactivity (240-300 mu C/ mu g). Low amounts of carrierfree I/sup 131/ iodide (2 mC) are allowed to react, without prior treatment, with small quantities of protein (5 mu g) in a highyield reaction (approx. 70% transfer of I/sup 131/ 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 I/sup 131/ iodide. The I/sup 131/-labeled hormone (up to 300 mu C/ mu g) contains no detectable degradation products and is immunologically identical with the unlabeled hormone. The loss of immunological reactivity at high specific radioactivities or at high levels of chemical substitution with STAI/sup 127/!iodine is demonstrated. (auth)

although it was unretarded on Sephadex G-200. It did not react with antiserum raised against standard growth hormone. Growth-hormone preparations (peak II) obtained from such Sephadex columns have not been used as standards in the present assay but have been used in the preparation of 1311-labelled growth hormone. In an experi- ment carried out in conjunction with Dr H. E. C. Cargill Thompson (Clinical Endocrinology Research Unit, Edin- burgh), peak I and peak II materials were assayed in terms of the starting material by the radio-immunoassay and by the tibia-line bioassay. Peak I was immunologically 18-4% and biologically 19-7% (fiducial limits 13-30%) of the starting material. Peak II was immunologically 120 % and biologically 142% (fiducial limits 111-228%) of the starting material.