Determine the sequence of a linear, unbranched hexapeptide for which the following experiments have been done:
1. Amino acid analysis : Phe, Ala, Ile, Arg, Lys, Met,
2. CNBr treatment : tetrapeptide (UV absorbance at 260nm), dipeptide
3. V8 protease cleavage : No cleavage
4. Trypsin cleavage : tripeptide (UV absorbance at 260nm), tripeptide
5. Chymotrypsin cleavage : tetrapeptide (UV absorbance at 260nm), dipeptide
6. Treatment with phenylisothicyanate gave a PTH derivative indicative of Ile
7. Treatment with carboxypeptidase Y, followed by phenylisothiocyanate gave a PTH derivative indicative of Lys
=> Give the sequence in three-letter code separated by dashes. Example Ala-Ala-Val-Ile. Must contain 6 amino acids from the list above from N-terminal to C-terminal. Make sure there is no typo, or you will get zero point. Only a perfect match will give you points.
my answer; Ala-Lys-Arg-Met-IIe is it correct?
To determine the sequence of the hexapeptide, let's go through each experiment and analyze the results step by step:
1. Amino acid analysis: The experiment shows the presence of six amino acids: Phe, Ala, Ile, Arg, Lys, Met.
2. CNBr treatment: The CNBr treatment resulted in the formation of a tetrapeptide and a dipeptide. We can assume that two amino acids reacted with CNBr to form the tetrapeptide, and the remaining two amino acids formed the dipeptide. Therefore, we know that at least four amino acids have been identified.
3. V8 protease cleavage: No cleavage occurred, indicating that the hexapeptide does not contain the specific cleavage site for V8 protease.
4. Trypsin cleavage: Trypsin cleaved the hexapeptide into a tripeptide and another tripeptide. This means that the hexapeptide must contain at least one tryptic cleavage site, resulting in the cleavage into two tripeptides.
5. Chymotrypsin cleavage: Chymotrypsin cleaved the hexapeptide into a tetrapeptide and a dipeptide. Similarly to the previous step, this indicates the presence of a chymotryptic cleavage site in the hexapeptide.
6. Treatment with phenylisothicyanate (PTC): When treated with PTC, the hexapeptide gave a PTH derivative indicative of Ile. This tells us that Ile is present in the hexapeptide.
7. Treatment with carboxypeptidase Y (CPY): Treatment with CPY, followed by PTC, resulted in a PTH derivative indicative of Lys. This means that Lys is also present in the hexapeptide.
Based on the information gathered from the experiments, we can conclude the sequence of the hexapeptide:
Ala-Lys-Arg-[unknown]-Ile-[unknown]
Note that we still have one unknown amino acid remaining. Unfortunately, the given information does not allow us to determine the exact identity of this amino acid.