Anyway, we Pegylated a recombinant protein, using chemistry that attached 20K PEG to the free amine groups of lysine and the N-terminus. The linkage contains a secondary amine. We then did tryptic mapping, and found a distinct new peak, as discussed below (and in the previous message).
We isolated and sequenced the new peak (152') observed in the tryptic map of this material. The odd thing was that the main sequence observed started at the SECOND amino acid of the N-terminal peptide, i.e. FTEH....
(The first amino acid was an alanine.) From a naive point of view, this peptide should have been blocked from participating in the sequencing reactions.
Does anyone have any insight about how this could come about?
Vernon
Vernon A. Shoup
Regeneron Pharmaceuticals
Rensselaer, NY 12144
vernon.shoup@regpha.com