Amino acid analysis of a nonapeptide yielded the following: Gly2, Glu, Met2, Lys

Question

Amino acid analysis of a nonapeptide yielded the following: Gly2, Glu, Met2, Lys, Arg2, Thr (the subscript 2's meaning two of that type of amino acid; e.g., two glycines, two methionines, and two arginines). Reaction of the intact nonapeptide with Sanger's reagent yielded FDNB-Arg; incubation with trypsin yielded free Arg, free Glu, a tripeptide, and a tetrapeptide. Reaction of the tripeptide with Sanger's reagent yielded FDNB-Gly, and reaction of the tetrapeptide with Sanger's yielded FDNB-Thr. Incubation of the above tripeptide with carboxypeptidase (identifies the C-terminal amino acid) identified Arg. Incubation of the above tetrapeptide with carboxypeptidase identified Lys. Reaction of the intact nonapeptide with cyanogen bromide yielded a tetrapeptide, a tripeptide, and a dipeptide. The dipeptide contained Arg and Glu, and the tetrapeptide also contained an Arg. Given this information, what is the sequence of nonapeptide? Enter the answer using the one-letter code.

Explanation / Answer

Sanger reagent is used to determine N-terminal amino acid of polypeptide chain.

Reaction of the intact nonapeptide with Sanger's reagent yielded FDNB-Arg. So, end teriminal of nonapeptide is R (Arg)

Cyanogen bromide hydrolyzes peptide bonds at the C-terminus of methionine residues. Reaction of the intact nonapeptide with cyanogen bromide yielded a tetrapeptide, a tripeptide, and a dipeptide and dipeptide is Arg and Glu and tetrapeptide contains Arg

            So, sequence becomes

Arg _ _ Met _ _ Met Arg Glu

Or

Arg _ _ Met _ _ Met Glu Arg

Trypsin cleaves c-terminal to Arginine and Lysine Residues

yielded free Arg, free Glu, a tripeptide, and a tetrapeptide

So, correct sequence is

Arg _ _ Met _ _ Met Arg Glu

Full nonapeptide sequence is-

R-T-G-M-K-G-M-R-Q

Cyanogen bromide hydrolysis will yield

Tetrapeptide- R-T-G-M

Tripeptide-K-G-M

Dipeptide- R-Q

Trypsin hydrolysis

First c-terimnal to arginine, it will yield free Glu and octapeptide, then octapeptide will be hydrolyzed at lysine.

Tripeptide: G-M-R

Tetrapetide: T-G-M-K

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.