Protein Radioiodination in a Radioassay Laboratory: Evaluation of Commercial Na¹²⁵I Reagents and Related Biohazards

Three commercial Na¹²⁵I solutions (Amersham, New England Nuclear, and Union Carbide) have been examined with respect to multiple parameters affecting their use in the radioiodination of three representative peptides (insulin, growth hormone, and gastrin): % of radioiodine incorporation in protein; immunoreactivity and non-specific binding properties of the radiolabeled proteins; pH, volatility, and radionuclidic purity of radioiodine solutions; and vial construction with respect to multidose use. All three commercial Na¹²⁵I produced radioiodinated proteins of good quality for use in radioligand assays. The radioiodines differed with respect to the amount of iodine released during initial vial opening as a consequence of different pH levels: 15 nCi/mCi (pH 12.5) to 1.0 uCi/mCi (pH 7.5). Two of the three products were shipped in vials with poor construction with respect to multi-dose use. Selection of a radioiodine was therefore reduced to the secondary considerations of iodine volatility and vial construction. The volatilized radioiodine observed during the spill of millicuries quantities of unbuffered pH 7.5 Na¹-²⁵! was 14 microcuries per millicurie within the first 30 minutes. One thickness of rubber gloves reduced potential skin contamination from an accidental spill to insignificant levels: 20–30 picocuries per microcurie. Common good housekeeping procedures: I.e. rubber gloves, laboratory coat and a fume hood were found to be sufficient protection to eliminate most radioiodine volatility and contamination hazards associated with protein radiolabeling procedures.