A heptapeptide was found to have an amino acid composition of asp. leu, lys, met

Question

A heptapeptide was found to have an amino acid composition of asp. leu, lys, met,phe and tyr.

Trypsin has no effect on the heptapeptide.

One cycle of Edman degradation renders the product whose structure is shown below.

Chymotrypsin treatment yields a dipeptide and a tetrapeptide, as well as a free amino acid.

The tetrapeptide is known to contain asp, leu, lys, and met.

Cyanogen bromide treatment generates a dipeptide that is determined to originate from the N-terminus of the heptapetide, a tetrapeptide, and free lys.

The peptide sequence in single letter amino code is ___________________.

Explanation / Answer

Chmyotrypsin gave dipeptide which means Phe is at second position where it will be cleved.

CNBr- cleves at methionine group , hence it was present at last but one and anothe Met at after 4 positions from start , hence we get free Lys

Thus Met at 4th , 6 positions and Phe at 2nd position, Lys is at 7th poistion

tetrapeptide obtained by chymotripsin which means Tyr is at 3rd which also gives free Tyr.

now sequence is Asp- Phe-Tyr-Met-Leu-Met-Lys

now we can see Chymotrypsin gives Asp-Phe + Tyr+ Met-Leu-Met-Lys

CNBr- gives Asp-Phe-Tyr-Met + Leu-Met+ Lys

now sequence is Asp-Phe-Tyr-Met-Leu-Met-Lys

( Edman degradation product not given in question hence Asp , Leu place cannot be fixed)

single letter code - D-F-Y-M-L-M-K ( or L-F-T-M-D-M-K)

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