Specific electrochemical iodination of horse heart myoglobin at tyrosine 103 as determined by Fourier transform ion cyclotron resonance mass spectrometry

Jesus Iniesta,Helen J Cooper,Alan G Marshall,John Heptinstall,David J Walton,Ian R Peterson

doi:10.1016/j.abb.2008.02.032

Abstract

The iodination of proteins remains a useful tool in biochemistry for radiolabelling. However, chemical or enzymatic iodination is difficult to control and can give deleterious polyiodination. Previously, we have shown that electrooxidation with nitrite is a rapid method for the selective nitration of tyrosine residues in proteins. In principle, it should be possible to substitute a number of electrooxidisable anions into the tyrosine phenol ring.Electrochemical iodination is more difficult to control than nitration because the rapid anodic oxidation of I− leads to persistent formation of the iodinating triiodide anion. However, application of pulsed electrooxidation and reduction cycles is shown to be an effective procedure for the selective mono and double-iodination of myoglobin, which may have general application to other proteins in controlling of the level of iodination.Mono- and double-iodination of myoglobin by this method was confirmed by electrospray FT-ICR mass spectrometry. Infrared multiphoton dissociation (IRMPD) enabled localization of the site of mono-iodination to be restricted to either His97 or Tyr103. More extensive sequence coverage was obtained with electron capture dissociation (ECD), allowing unambiguous assignment of the site of iodination to Tyr103.

Highlights

Iodination of proteins is an important tool in radioimmunoassays (e.g., [1]), receptor binding [2], determination of protein structure [3], production of radioactive peptide imaging agents [4] and generally as a marker for proteins [5,6]
We present a new electrochemical procedure for the selective mono and diiodination of horse heart myoglobin (Mb), in which the iodide concentration can be elevated, leading to a specific and selective tyrosyl iodination at residue Y103
Specific mono- and double-iodination of the protein was confirmed by use of electrospray Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry [18]

Summary

Introduction

Iodination of proteins is an important tool in radioimmunoassays (e.g., [1]), receptor binding [2], determination of protein structure [3], production of radioactive peptide imaging agents [4] and generally as a marker for proteins [5,6].

Results

Conclusion