Treatment of a polypeptide with 2-mercaptoethanol yields two polypeptides: A) Va

Question

Treatment of a polypeptide with 2-mercaptoethanol yields two polypeptides:
A) Val-Met-Cys-Arg-Gly-Gly-Phe-Arg-Cys-Leu-Ser

B) Gly-Gln-Asp-Cys-Tyr-Val-Ile-Lys-Glu-Cys-Thr

treatment with trypsin yileds fragments with the following amino acid composition:

Arg, Cys2, Glu, Met, Thr, Val

Arg, Gly2, Phe

Asp, Cys2, Gln, Gly, Ile, Leu, Lys, Ser, Tyr, Val

using the polypeptides above (A and B), indicate the positions of the disulfide bonds in the intact polypeptide.

Please explain the answer, and include the structure of the intact polypeptide.

Explanation / Answer

the role of 2-mercaptoethanol is to act as a reducing agent and break down disulfide bonds i.e. to break S-S bond and produce SH and SH ends.

cysteine has sulfide ends which help in forming disulfide bridges. when treated with 2-mercaptoethanol these disulfide bridges will be broken. thus yeilding two polypeptides.

A and B. intact polypeptide will be Val-Met-cys-arg-gly-gly-phe-arg-cys-leu-ser

                                                   Gly-gln-asp-cys-try-val-ile-lys glu-cys-thr.

peptide A is joined to the peptide B by 2 cys- cys bridges between Met-cys-arg and asp-cys-try and between arg-cys-leu   & glu-cys-thr

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