A nonapeptide was determined to have the following amino acid composition: (Lys)
ID: 817850 • Letter: A
Question
A nonapeptide was determined to have the following amino acid composition: (Lys)2, (Gly) 1, (Phe) 1, (His)1, (Val)3, Met. The native peptide was incubated with 1-fluoro-2,4-dinitrobenzene (FDNB) and then hydrolyzed; 2,4-dinitrophenylhistidine was identified by HPLC. When the native peptide was exposed to cyanogen bromide (CNBr), an octapeptide and free glycine were recovered. Incubation of the native peptide with trypsin gave a pentapeptide, a tripeptide, and free Lys. 2,4-Dinitrophenyl-histidine was recovered from the pentapeptide, and 2,4-dinitrophenylphenylalanine was recovered from the tripeptideThe native sequence was determined to be:
Answer
His-Val-Val-Val-Lys-Lys-Phe-Met-Gly
Would you please explain how this is done, thank you!
Explanation / Answer
2,4 Dinitroflorobenzene reacts with N termial of amino acid sequence and when hydrolysed N terminal amino acid remains and remaining all gets dissociated. Since hydrolsysed product is 2,4 dinitrophenyl-histidine N terminal amino acid is Histidine.
CnBr reacts with methionine group and cleaves after met group in sequence. Since we got free Gly . Gly is present aat end and Met is present before Gly.
Trypsin cleaves at base amino acid like Lys or Arg. Since we have Lys free and pentapetide and tri peptide as products . This indicates Lys is adjacent to Lys. And there are 4 amino acid left to Lys-Lys. and 3 amino acid left to Lys-Lys.
Since 2,4 dinitrophenyl phenyl alanine is recovered from tripeptide we have Phenyl alanine in tripeptide.
This must be before Met-Gly. Hence tri peptide sequence is Phe-Met-Gly.
By above we can conclude aequence
His -( 3 amion acid) )-Lys-Lys-Phe-Met-Gly.
since we are left with 3 valine . These valine fit into those 3 amino acids
hence His-Val-Val-Val-Lys-Lys-Phe-Met-Gly is sequence
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