Iodination involves the introduction of radioactive iodine into certain amino acids (usually tyrosines) in proteins and peptides. Iodination takes place at the positions orthogonal to the hydroxyl group on tyrosine; mono- or di-substitution can occur. When iodinatable sites such as tyrosines are absent or of limited accessibility, iodinatable phenolic sites can be introduced by using the Bolton-Hunter Reagents (SHPP and Sulfo-SHPP). Certain crosslinkers also contain iodinatable tyrosyl groups in their spacer arms.

Radioactive I-125 or I-131 can be incorporated into proteins either by enzymatic or chemical oxidation. In the chemical oxidation method, sodium iodide is converted to its corresponding reactive iodine form, which then spontaneously incorporates into tyrosyl groups. While necessary for iodine activation, oxidizing reagents are potentially damaging to proteins.

Comparison of Thermo Scientific™ Pierce™ iodination products

  Iodination reagent Iodination tubes Iodination beads
Detergent compatible

Denaturant compatible

pH range 4.4 to 9.0
(8 to 9 optimum)
4.4 to 9.0
(8 to 9 optimum)
4.0 to 8.5
(5.0 to 6.5 optimum)
Stability Stable indefinitely Stable indefinitely One year
Ease of use Requires good
plating technique
Easy Easy
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