Nick Theodorakis nicholas_theodorakis at
Tue Aug 31 09:50:33 EST 1999

In article <37CBC7DE.3A6EE922 at>,
  Frank.Fackelmayer at wrote:
> "Ian A. York" wrote:
> > In article <62fx3.944$2%3.6496215 at>,
> > Achim Recktenwald, PhD <ARecktenwald at> wrote:
> > >Martin Offterdinger <a8803349.nospam at> wrote in message
> > >news:37c524f5.342622 at
> > >> What is the purpose in using iodoacetamide for protein isolation. (I
> > >
> > >Iodoacetamide is an alkylating reagent for cysteines.
> > >Strange to use it during a protein purification. Normally it's used to
> >
> > Iodoacetamide is (among many other things) a protease inhibitor,
> > irreversibly inhibiting (not surprisingly) cysteine proteases.  It's often
> > used in protein purification for exactly that reason.
> >
> > Ian
> >
> Hi Ian,
> I also know iodoacetamide as an alkylating reagent for cysteines, but have
> not been aware of its use as protease inhibitor. Its action against cysteine
> proteases is plausible, of course, even though it might not be desirable to
> irreversibly modify cysteines on the protein that is to be purified.... Can
> you give use references as to the concentration people use to use for this
> purpose? Somewhere in the millimolar range?
> Frank

According to Calbiochem's Protease guide:
both bromelain, a cysteine protease, and carboxypeptidase P, a serine
protease (!) are inhibited by iodoacetate. They don't list the IC50,

I'm not sure I would use it in the isolation of any protein found in the
cytoplasm or other reducing milieu, though.

Interestly, bromelain is also inhibited by TPCK and TLCK. I don't know
much about cysteine proteases; might I assume that the -SH plays a
similar catalytic role that the -OH does in serine proteases?

| Nick Theodorakis                              |
| nicholas_theodorakis at       |
| (previously theodorn at    |

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