How can I quantify the number of free thiol groups on small peptides?

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Gerardo Ferrer-Sueta

Ellman's is the most popular by far, but I prefer 4-dithiodipyridine, which is faster and more sensitive. Here is a comparison of both methods.

http://www.ncbi.nlm.nih.gov/pubmed/?term=12110978

There is a modified method for enhanced sensitivity here

http://www.ncbi.nlm.nih.gov/pubmed/?term=17286954

I use the simple version practically on a daily basis and it works great. Of course there are many other methods for quantitating thiols.

Artur Ribeiro

Thanks a lot for the help