David,
I don't know if this is an option but Pierce sells 3 Biotin reagents
specifically designed to react with protein/peptide SH groups, i.e., cysteine.
Biotin-BMCC with a maleimide functionality,
Biotin-HPDP with a disulfide functionality, and
Biotin-LC-IA with an iodoacetyl functionality.
I have used the last reagent to quantitatively incorporate biotin on 3
distinct C-terminal cysteine synthetic peptides. Contact me if you would
like more info.
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