What is the pI for Lys-Glu-Ser?

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Expert Solution

Lys-Glu-Ser peptide is which can be represented as ,simply

Now, the cationic and/or anionic forms of Lys-Glu-Ser upon pH changing are given as

Hence, from the above pH values we can determine the pK_a s of the corresponding functional groups as followsFrom the definition of the isoelectric point we know that

where, pK₁ and pK₂ are the pK_a values of the monocation and monoanion form and from the above pH diagram it is clear that if we consider the overall neutral form which is created via step-B from monocation and destroyed via step-C to monoanion. So, the two pK_a s that we are looking for are the pK_a of the terminal NH₂ ie. 8.5 and the the pKa of the branched COOH ie. 3.5. So, from the formula we can calculate the Pⁱ of the peptide

queen_honey_blossom answered 1 year ago

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