Iodination of proteins by IPy₂BF₄, a new tool in protein chemistry

Iodination is a very useful method for protein characterization and labeling. However, derivatization chemistries used in most conventional iodination procedures may cause substantial alterations in protein structure and function. The IPy₂BP₄ reagent [bis(pyridine)iodonium (I) tetrafluoroborate] has been shown to be an effective iodinating reagent for peptides. Herein we report the first application of IPy₂BF ₄ in protein iodination in an aqueous medium using three representative substrates: insulin, lysozyme, and the enzyme 1,3-1,4-β-D-4-glucanohydrolase. Our results show that IPy ₂BF₄ has clear advantages over existing methods in that the reaction is quantitative, fast, and selective for the most accessible Tyr residues of a protein, and it preserves the functional integrity of the protein when moderate Tyr labeling levels are pursued.