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Specialty Chemistry Forums => Biochemistry and Chemical Biology Forum => Topic started by: NewtoAtoms on April 05, 2009, 11:43:13 AM

Title: Peptide sequencing..
Post by: NewtoAtoms on April 05, 2009, 11:43:13 AM

A pentapeptide was found to contain the amino acids Phe, Gly, Met, Ala, Ser.
N-terminal analysis yielded the PTH derivative of alanine.
Partial hydrolysis of the pentapeptide yielded the dipeptides (Gly-Ser)(Ala-Gly)(Ser-Met)
The peptide sequence is:

a.  Ala-gly-Ser-Phe-Met
b.  Ala-Gly-Ser-Met-Phe
c.  Phe-Ser-Gly-Met-Ala
d.  Phe-Met-Ser-Gly-Ala
e.  Phe-Ala-Gly-Ser-Met

Now I am a TAD bit confused in this question as I dont know where to place the Phe.
I have done the leg work so please let me explain:

The N-terminal analysis yielded the PTH derivative of alanine, therefore Ala, would be located on the far left. 
Sequencing the amino acids uncovers :

              Ser - Met
      Gly - Ser
Ala-Gly
---------------------
Ala-Gly-Ser-Met

However where on earth do I put the Phe??
I have thought this through immensely and have come to these conclusions:

a.  Ala-gly-Ser-Phe-Met        NO because it isn't in the partial hydrolysis dipeptide sequnces
b.  Ala-Gly-Ser-Met-Phe        PERHAPS but it doens't show the Phe in the sequencing....
c.  Phe-Ser-Gly-Met-Ala        NO OUT OF ORDER
d.  Phe-Met-Ser-Gly-Ala        NO OUT OF ORDER
e.  Phe-Ala-Gly-Ser-Met       THIS IS THE CORRECT ANSWER, because it isn't in the sequencing, the Phe was removed first in the previous PTH derivative????

any help would be GREATLY appreciated!

Newtoatoms

Title: Re: Peptide sequencing..
Post by: sjb on April 05, 2009, 01:02:34 PM

I'd actually suggest that you have this the wrong way around, and that b is the correct answer.

You've shown that Ala is the N-terminus, and that this is connected to Gly, which in turn is connected to Ser and then Met, so what's left is the Phe.

Title: Re: Peptide sequencing..
Post by: aHerraez on April 14, 2009, 06:52:48 AM

1.

Quote from: NewtoAtoms on April 05, 2009, 11:43:13 AM

The N-terminal analysis yielded the PTH derivative of alanine, therefore Ala, would be located on the far left.

That's definitive; so, you cannot put Phe before Ala.


2.

Quote from: NewtoAtoms on April 05, 2009, 11:43:13 AM

Sequencing the amino acids uncovers :

There is no sequencing done, they just give you some peptides resulting from hydrolysis (which clearly are NOT all the products from the hydrolysis, as they lack Phe)