Consider the following peptide: Cys-Arg-Pro-Asp-Thr-Leu-His-Lys-Gln-Glu-His How is the peptide different at pH = 6 and pH...

Consider the following peptide: Cys-Arg-Pro-Asp-Thr-Leu-His-Lys-Gln-Glu-His

How is the peptide different at pH = 6 and pH 8? Which of the two pHs would you use to run an ion exchange column, and would you choose anion or cation exchange?

Solutions

Expert Solution

Given peptide is Cys-Arg-Pro-Asp-Thr-Leu-His-Lys-Gln-Glu-His.

To answer the first question, we should know the isoelectric point of each enzyme.

AA Cys- Arg- Pro- Asp- Thr- Leu- His- Lys- Gln- Glu- His

pI 5.07 - 10.76 - 6.30 - 2.77 - 5.60 - 5.98 - 7.59 - 9.74 - 5.65 - 3.22 - 7.59

When the pH is lower than the pI, the amino acid will carry a net positive charge. When the pH is higher than pI, then the amino acid carries a net negative charge.

At pH = 6 given peptide will be having positive charge as more of amino acid have pI less than pH.

At pH = 8 magnitude of positive charge on the peptide will be increased as more amino acids pI become less than 8.

Choice of buffer pH is also needed to choose pH between 6 and 8.

If we look closely net charge on the molecule is positive. Therefore we will be choosing cation exchanger resin. pH should be below the pI of molecule of interest by 0.5-1.5 units.

So we will use pH = 6.

queen_honey_blossom answered 1 year ago

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