An unknown amino acid possesses a strongly basic side-chain amino group. Its acid dissociation constants are: , , and . Calculate the exact isoelectric point (pI) of this specific amino acid.

Question

An unknown amino acid possesses a strongly basic side-chain amino group. Its acid dissociation constants are: $pKa_1 (\alpha-COOH) = 2.2$, $pKa_2 (\alpha-NH_3^+) = 9.0$, and $pKa_3 (	ext{side-chain } NH_3^+) = 10.5$. Calculate the exact isoelectric point (pI) of this specific amino acid.

Prashant Kotian · Accepted Answer

Correct answer: C. For basic amino acids possessing an extra ionizable amino group (like Lysine), the isoelectric point () is the arithmetic mean of the two highest basic values (the ones bracketing the neutral zwitterion state). .

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