The acidic dissociation constants for valine are (for the carboxyl group) and (for the ammonium grou β Biomolecules Chemistry Question
Question
The acidic dissociation constants for valine are $pKa_1 = 2.30$ (for the carboxyl group) and $pKa_2 = 9.70$ (for the ammonium group). Compute the exact isoelectric point ($pI$) of valine.
Answer: 6
π‘ Solution & Explanation
For an amino acid with an uncharged (neutral) non-ionizable side chain like valine, the isoelectric point ($pI$) is merely the arithmetic mean of the two core $pKa$ values surrounding the zwitterion phase. $pI = \frac{pKa_1 + pKa_2}{2} = \frac{2.30 + 9.70}{2} = \frac{12.00}{2} = 6.00$.
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