Electrolytic preparation of bioactive radioiodinated parathyroid hormone of high specific activity

A technique for the preparation of microgram quantities of bovine parathyroid hormone (bPTH) labeled with carrier-free 125I to a specific activity of 1300 Ci/mmol is described. A restructured and simplified apparatus was used for electrolytic iodination, making it feasible to use reaction volumes of 100 to 200 ml. The miniaturized setup requires only a small platinum crucible connected via an agar-KCl salt bridge to a saturated KCl solution, a battery to drive the reaction, and a voltmeter to monitor the potential difference between the reference-saturated KCl solution (via a calomel electrode) and the platinum crucible. The [125I]-labeled bPTH elutes as a single species when chromatographed on a Biogel P-10 column equilibrated in 3 M guanidine HCl-2.3 M formic acid, and it retains full biologic activity when bioassayed in vivo. It is evident that bPTH labeled to a high specific activity with 125I does not suffer in regard to its biological potency