Comparison of specific radioactivities of human alpha-lactalbumin iodinated by three different methods

Radioiodination provides an extremely sensitive method for the detection of low levels of proteins. In the development of a sensitive radioimmunoassay for human alpha-lactalbumin (alpha-LA), the protein was labeled to high specific activity (approaching 2000 Ci/mmol) with lactoperoxidase, chloramine-T, and Iodogen. Despite high specific activities of the labeled protein by each method, there was a considerable difference in their binding affinity with monoclonal anti-human alpha-LA antibodies due to varying degrees of protein damage. Iodination of human alpha-LA with Iodogen resulted in labels of the highest specific activity and immunoreactivity with the monoclonal antibodies used.