How to block free SH groups?

WS via (by novalidaddress from
Thu Apr 21 08:06:17 EST 2011

Dear experts,

I have question, possible somewhat related to Sudheer's, in an
inversed way:

I would like to block free SH-groups in a solution that contains
antibodies. I am looking for something that happily will react with
free sulfhydryls, but dos not reduce disulfide bonds. I shortly
thought of TCEP, but this used as reducting agent. Maleimides are used
to label proteins at SH-groups - will they reduce SS bonds? What about
NBD-F (Nitrobenzo-oxadiazole, a reagent for quantifying SH-groups).
Iodo-acetamide? I also would like to avoid simultaneous reaction with
amino groups (from eg lysines). Possible buffers are PBS, slightly
alkaline borate or tris @ pH7.5. Of course, excess reagent should be
easy to quench and/or remove by gel filtration.

Any ideas, suggestions, comments?

Thank you all,



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