An Octapeptide Was Determined to Have the Following Amino Acid

question 103

Multiple Choice

An octapeptide was determined to have the following amino acid composition: Lys (2) ,Phe (2) ,Gly (1) ,His (1) ,Leu (1) ,Met (1) .The native peptide was run through one cycle of the Edman degradation and the PTH-leucine derivative was identified by HPLC.When the native peptide was exposed to cyanogen bromide (BrCN) ,a heptapeptide and free glycine were recovered.Incubation of the native protein with trypsin gave a tetrapeptide,a tripeptide,and free lysine.The peptides were separated and each run through one cycle of the Edman degradation.The tetrapeptide yielded the PTH-leucine derivative,and the tripeptide yielded the PTH-phenylalanine derivative.Incubation of the native protein with pepsin produced a dipeptide and two tripeptides.The amino acid composition of the tripeptides (not the order) were determined to be (Phe,Gly,Met) and (Phe,Lys,Lys) .What is the sequence of the octapeptide?
Specificities of Proteases
BrCN cuts at the C-terminal side of Met
Trypsin cuts at the C-terminal side of Lys or Arg
Pepsin cuts at the N-terminal side of Phe,Trp or Tyr

• A)Leu-His-Phe-Lys-Lys-Phe-Met-Gly
• B)Gly-Met-Phe-Lys-Lys-Phe-His-Leu
• C)Met-Leu-Phe-Lys-Phe-Gly-Lys-His
• D)Leu-His-Lys-Lys-Phe-Phe-Gly-Met
• E)His-Phe-Leu-Lys-Lys-Phe-Met-Gly

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Definitions:

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