Comparison of three iodination methods for human somatotropin.

Human somatotropin (growth hormone) iodinated by use of lactoperoxidase or Chloramine T added stoichiometrically has been compared with hormone iodinated by conventional Chloramine T method. The three preparations were indistinguishable, both in their stability to storage and in their suitability for use in radioimmunoassay. Degradation of tracer, as measured by decreasing precipitability with trichloroacetic acid, was found to be an unsatisfactory measure of immunoreactivity, because aggregates of high relative molecular mass formed during storage at--15 or--80 degrees C are less immunoreactive.