Thank you, I think that now I found a way to deal with this type of question. As you said, it is really the best way to start with the β-Mercaptoethanol and then to mud through the rest of the enzymes and peptides.
So here that means:
A: N - Met, Cys, Thr, Ile, Asp, Phe, Gly - C
B: N- Arg, Ile, Val und Cys -C
Firstly, I deal with A:
Edman tells us, which AA (amino acid, just to make it short) is the first from the N-terminal ending, in this case it's Ile for A.
1. Thr-Met-Cys-Ile-Asp-Phe-Gly
Now the Carboxypeptidase shows us the last AA, which is Ile
2. Thr-Met-Cys-Asp-Phe-Gly-Ile
BrCN cuts right after Met and the AA sequence is Cys-Ile, so we must have Met-Cys-Ile (Ile is also our last AA)
3. Thr-Asp-Phe-Gly-Met-Cys-Ile
The Chymotrypsine doesn't change much any more, but anyway our first three AA comply with the fact that Chymotrypsine gives us a peptide that consists of Thy, Phe, Asp.
In the solution they have Asn instead of Asp, but I think it's just a misspelling. So this would be the solution for A.
For B there is a quite similar procedure:
B: Arg, Ile, Val und Cys
Edmann + Caboxypeptidase give us the first and the last AA:
1. Ile-Arg-Cys-Val
Trypsin gives us Val AFTER an lysine or arginine, here we have Arg. Val stays at the C-end (just sayin' because first it thought to place Val just behind Arg, like Ile-Arg-Val-Cys, but that's wrong as Val has to be the last AA (Carboxypeptidase). So the right way would be:
2. Ile-Cys-Arg-Val
After that you have to put in the disulfide bond between the two Cys. Woohoo! Still, I would say this type of question leaves a lot of room to do mistakes, especially during a written exam. So after all, it s****
.
And thank you Irlanur for putting me on the right track!