I have a peptide sequence with no prolines, 2 positively charged residues at the c-terminal ends of 2 fragments created by trypsin cleavage, but shows no fragments from carboxypeptidases A or B. I thought if a positively charged residue was the c-terminal end of the primary peptide, then I should have seen fragments from carboxypeptidase B, since there is no blocking proline by either the Arg or Lys. I am stumped--what am I missing?