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Specialty Chemistry Forums => Biochemistry and Chemical Biology Forum => Topic started by: Rayan on September 09, 2005, 04:38:22 PM

Title: sequencing problem
Post by: Rayan on September 09, 2005, 04:38:22 PM

we propose to determine the structure of an oligopeptide D.

a- the action of b-mercaptoethanol on d gives 2 peptides A and B.

b- the mixture of peptides is treated with 6M HCl, it produces: trp, met, 2 cys, glu, phe, arg, NH4+

c- the carboxypeptidase is active on A but not on B>

d- Hydrolysis of A catalyzed by trypsin produces an amino acid and a dipeptide B1.
B1 migrates to the anode during the electrophoresis in buffer pH=6.5.
the action of FDNB on peptide B produces DNP-cys.

e- 2 peptides A1 and A2 are produced after treatment of peptide A by chymotrypsin. they are separated then put in strong basic solution and at the end treated by strong acidic solution. we need 2 times more strong acid to titrate completely identical quantity of the dipeptides. action of sanger reagent on A2 liberates DNP-cys.
peptide B does not contain a hetercyclic nucleus.

Give the structure of the oligopeptide D.

i came up with:

arg, trp, cys, cys ( met phe glu) NH4+

i couldn't determine the order of met phe and glu. so would anyone help me?

ps: sorry for the long message.