Protein purification: iodoacetic acid -does it stuff up cysteines

Cornelius Krasel krasel at
Fri Feb 24 15:49:20 EST 1995

Orak (Ross.Thomas at wrote:
> I have been using iodoacetic acid (IAA) as a protease inhibitor for purifying
> recombinant transcription factors.  However, someone recently told me
> that IAA works by modifying cysteine residues.  Can someone confirm this
> for me? 

That's what I have learned when I was still a student. Look up Stryer
or other biochemistry books. The alpha-C in IAA is very poor in electrons,
therefor it easily forms covalent bonds with electron-rich partners,
such as the sulfur in Cys or the N in His. These alkylation reactions
are essentially irreversible.


/* Cornelius Krasel, Abt. Lohse, Genzentrum, D-82152 Martinsried, Germany  */
/* email: krasel at                 fax: +49 89 8578 3795  */
/* "Science is the game you play with God to find out what His rules are." */

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