Another option is DTNB (aka Ellman's Reagent). This compound reacts with free thiols and produces a yellow color. The reaction is stoichiometric, so if you have access to a very basic spectrophotometer and know your protein concentration you can quantify the free thiols quite easily.
Basic pH doesn't break disulfides, if anything it stabilizes them. I would be more concerned that they are incorrectly formed as described by Herman.
Mike
----- Original Message -----
From: "D Bonsor" <[log in to unmask]>
To: [log in to unmask]
Sent: Friday, August 19, 2011 6:21:41 AM GMT -08:00 US/Canada Pacific
Subject: Re: [ccp4bb] Off topic_protein degradation.
If you are unsure about whether the disulfides have formed treat a small amount of protein with N-ethylmaleimide. If the disulfides have not formed, when you perform mass spec on the protein you should see an increase of mass of 125Da for each exposed cysteine.
--
Michael C. Thompson
Graduate Student
Biochemistry & Molecular Biology Division
Department of Chemistry & Biochemistry
University of California, Los Angeles
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