Henry,
Here are some suggestions in no particular order of chance of success:
1) label the amine(s) with a UV or fluorescent derivatizing agent and
compare to a peptide with known concentration and # of amines. Many out
there to choose from! Assumes quantitative reaction!!!
2) completely reduce all three -SS- bonds and derivatize with a thiol
specific reagent, e.g., Ellman's reagent. Assumes quantitative reaction!!!
3) the -SS- bond absorbs at ~246 nm but with a poor extinction coefficient
(<1,000). If you are sure your peptide has all thiols linked AND you have
sufficient quanitity, then this might work if the peptide contains no other
chromophores in this region of the spectra. I have used this procedure
before with a 4-channel HPLC detector and obtained satisfactory results.
Regards,
Dan L. Crimmins
Washington University School of Medicine
Dept. Pathology/Division of Laboratory Medicine
660 S. Euclid Ave., Box 8118
St. Louis, MO 63110
Phone: 314-454-8514; Fax: 314-454-5208
e-mail: crimmins@labmed.wustl.edu