A peptide C was found to have a molecular mass of about 1000. Amino acid analysis of C revealed its composition to be (Ala₂,Arg,Gly,Ile). The peptide was unchanged on treatment with the Edman reagent, then CF₃CO₂H. Treatment of C with trypsin gave a single peptide D with an amino acid analysis identical to that of C. Three cycles of the Edman degradation applied to D revealed the partial sequence Ala-Ile-Gly.

(a) Suggest a structure for peptide C and explain how you arrived at that structure.

(b) Describe what you would expect to see for the b-type fragmentation of the M + 1 ion of both peptides C and D in MS–MS.