a) Using the mass of the final peptide piece and the information about B and Y ion fragments, propose the 9-amino acid primary sequence (use 3 letter codes). Please show all your working. Consider all the information provided in the question when deciphering the identity of the amino acids.

b) Draw the mechanism for the MS fragmentation of the peptide bond between the amino acids that are in positions 7 and 8 from the N-terminus. Make sure to show all steps and arrows. Label the resulting b7 and y2 ions. You can abbreviate the amino acids towards the N and C termini but the amino acids on either side of the cleavage site must be drawn out fully in your mechanism (include correct stereochemistry

You have an unknown protein whose sequence you want to determine. The protein is 200 aa long so you treat it with trypsin to break it into smaller pieces. After the trypsin digest, you obtain 10 peptide pieces and have determined the sequences of all but one. You determine the overall mass of your final peptide piece to be 1144.2m/z for a singly charged ion. You then run an MS/MS fragmentation experiment to confirm the primary sequence of this peptide. Shown in Figure 1 is the fragmentation information you obtain. Figure 1 Fragmentation of the final peptide showing observed b and y ions in black, grey ions were not observed and their mass is unknown