[Protein-analysis] Re: equilibrium const for disulfide bond formation

Uncle Al via proteins%40net.bio.net (by UncleAl0 At hate.spam.net)
Tue Jan 9 18:12:50 EST 2007

juicymixx At mailinator.com wrote:
> Hello,
> This is a pretty simple question; however I can't seem to find an
> answer to it.   I have a rather small protein (60 amino acids) in which
> I've mutated in a single cysteine for labeling purposes.   There are no
> other cysteines in the protein.   Additionally the protein is normally
> unstructured in solution (that is in 30uM phosphate buffer at 25C,
> there is no significant structure).   Recently we've noted that after
> purifying the protein (but before labeling it) we appear to have some
> dimer formation which isn't seen in the wild type protein.
> I was just wondering what the equilibrium constant (reaction rate,
> etc.) for intermolecular disulfide formation from 'free' cysteine would
> be (or better yet, cysteine in a polymer/peptide/protein).   Someone
> has probably already done this experiment, however I'm not sure of
> where to look for this number...

Work under inert gas, add some modest reducing agent.  Cysteine to
cystine is entirely reversible under mild conditions if not rpevented


At high concentrations it induces cleavage of disulfide bonds.  At low
concentrations it prevents oxidation of SH groups during
polyacrylamide gel electrophoresis.

Uncle Al
 (Toxic URL! Unsafe for children and most mammals)

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