I apologize if this is a stupid question, but did you incorporate a beta-amino
acid before the FITC? If not, then you could have reproduced edman degradation
(cyclization and cleavage) when you cleave the peptide from the resin.
Using FITC seems to be the most common way of labeling peptides with
fluorescein, but we've used a method that's much cheaper (always a bonus). We
buy fluorescein acid from Sigma (F7505, $11.35 for 100g) and couple it like an
amino acid. It's somewhat sterically hindered, so we might have to do double
couplings or use extended coupling times (2-4 h), but it saves so much money
that we feel it's worth it. Let me know if you have any questions.
Good luck!
Jeni
Janelle Lauer-Fields
Department of Chemistry & Biochemistry
Florida Atlantic University
777 Glades Road
Boca Raton, Florida 33431
561-297-2094/Fax 561-297-2759