Question

A heptapeptide is shown to have the amino acid composition: phenylalanine glutamate methionine valine lysine threonine and histidine.

I   treatment of the heptapeptide with cyanogen bromide yields a tetra and a tri-peptide

II treatment of the tetrapeptide with dansyl chloride yields the dansyl derivative of histidine upon acid hydrolysis

III treatment of the tetrapeptide with trypsin yields 2 dipeptides

IV treatment of the tripeptide with carboxy peptidase yields primarily valine

V a single round of Edman degradation of the tripeptide yields the phenylthiohydantoin (PTH) derivative of threonine

VI treatment of the original heptapeptide with lithium borohydride followed by acid hydrolysis yields the alcohol derivative of valine.

the sequence of the heptapeptide is

	a.	lysine methionine threonine phenylalanine glutamate valine histidine
	b.	threonine lysine methionine phenylalanine glutamate histidine valine
	c.	phenylalanine glutamate lysine methionine histidine threonine valine
	d.	valine glutamate threonine methionine phenylalanine lysine histidine
	e.	histidine lysine phenylalanine methionine threonine glutamate valine

Answer 1

the possible sequence is e) Histidene Lysine Phenylalanine Methionin Thereonine Glutamate Valine

Because The heptapeptide was cleaved by Cynogen bromide to give a tetra and a tripeptide the cleavage happens at methionine when CNBr is used. And the tetrapeptide gave dansyl histidine inicates the N termal is Histidine and the breakdown with trypsin cleaves at lysine hence indicating lysin at second position.

Formation of valine in tripeptid eon treatment with carboxy peptidase and Edmann degradation gives threonine indicates the N terminal of tripeptide is threonine since Edmann degraadation will cleave N terminal amino acid.