BIOCHEMISTRY QUESTION. HELP!!! Suppose you add the two peptide sequences shown b

Question

BIOCHEMISTRY QUESTION. HELP!!!

Suppose you add the two peptide sequences shown below to the enzyme chymotrypsin in a buffered solution that is composed of entirely of 'heavy' water (H2 18O)*. After adding the peptides to the chymotrypsin solution, using a mass spectrometer you observe that the mass of peptide 1 has shifted by two mass units (Daltons) relative to its normal mass. The mass of peptide 2 is unaffected. If you add these peptides to the same heavy water buffer without chymotrypsin present, neither peptide shows a mass shift. Explain this result based on what we know about chymotrypsin.

1) H2N-Ala-His-Thr-Phe-COOH

2) H2N-Ala-His-Thr-Lys-COOH

*Heavy water is exactly like normal water, except the oxygen incorporated into the water molecule exists as a stable isotopic variant, having two more neutrons (10 total) compared to normal oxygen (8 total). These two extra neutrons give heavy water a molecular weight two daltons more than normal water.

Explanation / Answer

Phylloxin, A, is a peptide isolated from the skin of the hylid frogs belonging to the genus Phyllomedusinae. Total acid hydrolysis results in the isolation of the following amino acids: A (Ala, Cys, Gly3 , Glu2 , Ile2 , Leu, Lys, Met, Phe, Ser3 , Tyr2 ) Use the information to establish the sequence of amino acids in phylloxin. Trypsin cleaves on the C-side of basic residue, ArgXaa and LysXaa CNBr cleaves on the C-side of methionine, MetXaa Chymotrypsin cleaves on the C-side of aromatic residues TyrXaa and PheXaa Fluorodinitobenzene and acid hydrolysis gives N-terminus DNP-Xaa derivative Edman degradation sequentially cleaves N-terminus residues Chymotrypsin digestion, separation of peptides, and Edman degradation give the following sequences for fragments:

Gly-Ala-Glu-Ala-Thr-Glu
Gly-Lys-Val-Gly-Ala-His-Ala-Gly-Glu-Tyr
Val-Leu-Ser-Pro-Ala-Lys-Thr-Asn-Val-Lys-Ala-Ala-Trp

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