title: Preparation of 125I-protein A usable for up to 10 months in immunoassays.
abstract: Chloramine-T iodination of protein A from Staphylococcus aureus and gel electrophoretic purification of the iodination mixture results in a stable tracer of high specific and functional activity. Following repeated gel electrophoresis of the tracer only a single component was observed. The specific activity of the 125I-protein A was between 30 and 55 muCi/micrograms. The binding of 125I-protein A to rabbit immunoglobulin exceeded 90% and the tracer competed effectively with unlabelled protein A in binding to cells incubated with sera containing surface antibodies. Storage of the tracer for up to 46 weeks resulted in a moderate decrease in maximal binding to immunoglobulin (from 91% to 64%), in TCA precipitable radioactivity (from 97% to 80%) and an approx. 30% decrease in the ability to detect cell bound immunoglobulin. It is concluded that gel electrophoretic purification of 125I-protein A produces a tracer with a very long shelf life.
mesh_terms: D002700:Chloramines / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D007457:Iodine Radioisotopes; D007553:Isotope Labeling; D013205:Staphylococcal Protein A; D014105:Tosyl Compounds
chemical_list: D002700:Chloramines; D007457:Iodine Radioisotopes; D013205:Staphylococcal Protein A; D014105:Tosyl Compounds; C016300:chloramine-T