A nonapeptide was determined to have the following amino acid composition (by hy

Question

A nonapeptide was determined to have the following amino acid composition (by hydrolyzing peptide in 6.7 M hydrochloric acid at 110 C for 22 hr, then identifying the amino acids via chromatographic separation): (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-dinitrophenlyhistidine was identified by HPLC. When the native peptide was exposed to cyanogen bromide (CNBr), an octapeptitde and free gylcine were recovered. Incubation of the native peptide with trypsin gave a pentapepotide, a tripeptide and a free lysine. 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. What is the sequence of the original native peptide?

Explanation / Answer

His-Leu-Phe-Gly-Lys-Lys-Phe-Met-Gly.

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