A sample of a peptide of unknown sequence was treated withtrypsin; another sample of the same peptide was treated withchymotripsin. The sequences (N-terminal to C-terminal) of thesmaller peptides produced by trypsin digestion were; Met-Val-Ser-Thr-Lys Val-Ile-Trp-Thr-Leu-Met-Ile Leu-Phe-Asn-Glu-Ser-Arg The sequence of the smaller peptides produced by chymotrypsindigestion were; Asn-Glu-Ser-Arg-Val-Ile-Trp Thr-Leu-Met-Ile Met-Val-Ser-Thr-Lys-Leu-Phe Write the sequence of this protein below; N.........................................................................................................C A sample of a peptide of unknown sequence was treated withtrypsin; another sample of the same peptide was treated withchymotripsin. The sequences (N-terminal to C-terminal) of thesmaller peptides produced by trypsin digestion were; Met-Val-Ser-Thr-Lys Val-Ile-Trp-Thr-Leu-Met-Ile Leu-Phe-Asn-Glu-Ser-Arg The sequence of the smaller peptides produced by chymotrypsindigestion were; Asn-Glu-Ser-Arg-Val-Ile-Trp Thr-Leu-Met-Ile Met-Val-Ser-Thr-Lys-Leu-Phe Write the sequence of this protein below; N.........................................................................................................C
Explanation / Answer
The fragments obtained from the trypsin digestion are: Met-Val-Ser-Thr-Lys Val-Ile-Trp-Thr-Leu-Met-Ile Leu-Phe-Asn-Glu-Ser-Arg As the enzyme trypsin cleaves at the carboxyl end of the aminoacids Lys and Arg there is one fragment which does not fit thiscriteria. It is the 2nd fragment.It ends in Ile. So we take it as the C-terminal amino acid. So we take it as the C-terminal amino acid. We see the results of the chymotrypsin digestion: Asn-Glu-Ser-Arg-Val-Ile-Trp Thr-Leu-Met-Ile Met-Val-Ser-Thr-Lys-Leu-Phe The enzyme cleaves only aromatic amino acids at their carboxylend. So two of the fragments fit this criteria but the 2nd fragmentends with Ile which is not an aromaticacid. So we can confirm that it is the C-terminal amino acid. The enzyme cleaves only aromatic amino acids at their carboxylend. So two of the fragments fit this criteria but the 2nd fragmentends with Ile which is not an aromaticacid. So we can confirm that it is the C-terminal amino acid. So now we know a part of the sequence: Val-Ile-Trp-Thr-Leu-Met-Ile We see a match for this sequence in the chymotrypsinresults: we see a match in the 1st fragment: Asn-Glu-Ser-Arg-Val-Ile-Trp So the present sequence is Asn-Glu-Ser-Arg-Val-Ile-Trp-Thr-Leu-Met-Ile We see a match for the sequence--Asn-Glu-Ser-Arg- we search in the trypsin results: we get a match in the 3rd fragment: Leu-Phe-Asn-Glu-Ser-Arg So the present sequence is Leu-Phe-Asn-Glu-Ser-Arg-Val-Ile-Trp-Thr-Leu-Met-Ile We search for the sequence----Leu-Phe-Asn we search in the chymotrypsin results: we get a match in the 3rd fragment: Met-Val-Ser-Thr-Lys-Leu-Phe so the present sequence is Met-Val-Ser-Thr-Lys-Leu-Phe-Asn-Glu-Ser-Arg-Val-Ile-Trp-Thr-Leu-Met-Ile So the sequence from N terminal to C terminal is: N'---Met-Val-Ser-Thr-Lys-Leu-Phe-Asn-Glu-Ser-Arg-Val-Ile-Trp-Thr-Leu-Met-Ile--C'