A Nonapeptide Was Determined to Have the Following Amino Acid

question 99

Multiple Choice

A nonapeptide was determined to have the following amino acid composition: (Lys) ₂, (Gly) ₂, (Phe) ₂, His, Leu, Met. The native peptide was incubated with 1-fluoro-2,4-dinitrobenzene (FDNB) and then hydrolyzed; 2,4-dinitrophenylhistidine was identified by HPLC. When the native peptide was exposed to cyanogen bromide (CNBr) , an octapeptide and free glycine were recovered. Incubation of the native peptide with trypsin gave a pentapeptide, a tripeptide, and free Lys. 2,4-Dinitrophenyl-histidine was recovered from the pentapeptide, and 2,4-dinitrophenylphenylalanine was recovered from the tripeptide. Digestion with the enzyme pepsin produced a dipeptide, a tripeptide, and a tetrapeptide. The tetrapeptide was composed of (Lys) ₂, Phe, and Gly. The native sequence was determined to be:

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

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