You have isolated a protein, but now need to determine the amino acid sequence.

Question

You have isolated a protein, but now need to determine the amino acid sequence. Your results are below: After one cycle of Edman degradation the phenylthiohydantoin, PTH, derivative below was produced:

You have isolated a protein, but now need to determine the amino add sequence. Your results are below: After one cycle of Edman degradation the phenylthiohydantoin, PTH, derivative below was produced: Treatment with cyanogen bromide gave the following fragments: KPAM PD LICWM TRM One of the fragments produced after treatment with chymotrypsin was: MPD Give the sequence of the peptide, using the one-letter abbreviations, no spaces.

Explanation / Answer

The amino acid associated with PTH is Threonine. Hence, threonine must be at the N-terminus.

Cyanogen bromide cleaves the peptide bond towards the C-terminus of Methionine.

Chymotrypsin cleaves the peptide bond at the C-terminus of an aromatic (hydrophobic amino acid).

If the amino acid has the following sequence, then the fragments are expected to come out as shown below:

H2N - TRMKPAMLICWMPD-COOH

Cyanogen bromide treatment of this peptide cleaves at the following retions and will give the following fragments:

H2N - TRM ' KPAM ' LICWM ' PD-COOH

H2N - TRM - COOH

H2N - KPAM - COOH

H2N - LICWM - COOH

H2N - PD - COOH

* Chymotrypsin will cleave the peptide at the positions shown below, and give the fragments:

H2N - TRMKPAMLICW ' MPD-COOH

Therefore, the correct sequence of amino acids is H2N TRMKPAMLICWMPD COOH

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