An Octapeptide Was Determined to Have the Following Amino Acid

question 29

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 CNBr) , 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:

Neutrons

Subatomic particles found in the nucleus of an atom with no electric charge.

Protons

Subatomic particles found in the nucleus of an atom, carrying a positive electrical charge.

Isotope

Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number, but have the same number of protons in their atomic nuclei.

Neutrons

Subatomic particles with no electrical charge, found in the nucleus of an atom, and responsible for much of the mass of atoms.