Iodination IODO-BEADS

Markwell (1982) reported that the reaction mechanism for creating the electrophilic iodine species may be somewhat different for IODO-BEADS than other oxidizing agents. She demonstrated that the active component remained at or near the... 

IODO-BEADS may be used in a variety of buffer salts and in the presence of detergents or denaturants without affecting iodination. The reagent, however, is susceptible to inactivation by reducing agents such as disulfide reductants, and it can be inactivated by moisture on storage. Also avoid organic solvents that can dissolve or affect the surface characteristics of polystyrene, such as DMF or DMSO. 

Figure 265 IODO-BEADS contains immobilized Chloramine-T functional groups that can react with radioactive iodide in aqueous solution to form a highly reactive intermediate. The active species may be an iodosulfonamide derivative, which then can iodinate tyrosine or histidine residues in proteins.

IODO-BEADS reaction from the manufacturer s recommended pH 7.0 to 8.2 (Tsomides et al., 1991). No reducing agent is required to stop the iodination reaction, as is the case with chloramine-T and other methods. Simple removal of the bead(s) from the reaction is enough to eliminate the iodination process. The mild nature of the IODO-BEADS iodination reaction can result in better recovery of active protein than using soluble oxidants (Lee and Griffiths, 1984). 

Wash one or more IODO-BEADS (Pierce) with the iodination buffer of choice. Buffers containing 0.1 M sodium phosphate or 0.1 M Tris at slightly acidic to slightly alkaline pH work well. A buffer consisting of 0.1 M sodium phosphate, pH 6.5, will give the highest possible reaction rates and yields. 

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