The purification and characterization of radiolabelled parathyroid hormone for radioimmunoassay

An improved method for the purification of 125I-labelled PTH is presented. Following iodination of the hormone by the chloramine-T method, the reaction mixture is transferred directly to a 0.9 x 9 cm column of carboxymethyl-cellulose. Two major peaks emerge with the ammonium acetate gradient. Peak I represents labelled intact bPTH, Msub(r) 9600, of good quality, i.e. a high B0 and a low NSB in the radioimmunoassay. Peak II, Msub(r) approximately 12000-18000, gives a high B0, but also a high NSB and is less suitable for RIA. Peak II is not the result of iodination damage, as it is also present in the unlabelled PTH (Inolex); it is suggested that it represents either a pre-prohormone or an aggregate of PTH. The label produced is usable for up to 3 months. Trasylol and benzamidine protect the label against proteolytic degradation equally well; the latter, however, is considerably cheaper. (Auth.)