Question #242686

Estimate the net charge of a Glu–Tyr dipeptide at pH 6.0.

Expert's answer

Find the **pKa** values for **Glu**

pK_{1} (alpha carboxylic group) - 2.19, **which is less than pH = 6, hence, the alpha carboxylic group will hold a negative (-1) charge.**

pK_{2} (Alpha amino group) - 9.67, **which is more than pH = 6, hence it will have a positive charge (+1).**

pK_{3} (side chain) - 4.25, **which is less than pH = 6, hence, the side chain carboxylic group will hold a negative (-1) charge.**

Now, the **pKa** values for **Tyr** are -

pK_{1} (alpha carboxylic group) - 2.20, **which is less than pH = 6, hence, the alpha carboxylic group will hold a negative (-1) charge.**

pK_{2} (Alpha amino group) - 9.11, **which is more than pH = 6, hence it will have a positive charge (+1).**

**Hence, the net charge of the dipeptide Glu-Tyr will be -**

**(-1) + (+1) + (-1) + (-1) + (+1) = -1.**

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