Protein hydrolysis

[NA19]

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This is part of a passage. Later on in the passage, there's a question and the answer key to the question says, based on this experiment, alanine cannot be on the C terminus. Can anyone explain why alanine can not be on the C-terminus?

 

[FeinMS]

C terminus means at the end of a peptide (remember N->C) However, from the given info, alanine is always followed by some other AA. Thus it can't be at the end.

 

[IcemanMD]

More specifically, the picture shows that there are 3 fragments that end or begin with alanine. Use this to conclude that alanine is the cleavage point for the chain.

If there were an alanine on the C terminus, then one the resulting fragments would be alanine by itself. Since this is untrue, alanine cannot be on the 'end' of the peptide or the C terminus.

ex
ser-x-ala--his--tyr-x-ala


Cleave at x
Resulting fragments:
1. ser
2. ala--his--tyr
3. ala

With the given fragments its not possible to have ala at the c terminus.

 

[NA19]

So what's the amino acid sequence? ser-ala-pro-ala-phe-gly?

 

[IcemanMD]

That is a possibility yes.