Lysine has pK_a values 2.18 (alpha-COOH), 8.95 (alpha-NH3+) and 10.53 (side-chain NH3+). Taking pI as the mean of the two pKa values flanking the net-neutral species, pI is

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JEE Advanced levelSingle correct optionDifficulty 3 of 3bm191

Lysine has $p K_{a}$ values $2.18$ ( $α$ -COOH), $8.95$ ( $α$ - $NH X_{3} X^{+}$ ) and $10.53$ (side-chain $NH X_{3} X^{+}$ ). Taking pI as the mean of the two pKa values flanking the net-neutral species, pI is

A5.56
B6.35
C7.22
D9.74

Answer: D

Net charge goes +2, +1, 0, -1 as pKa 2.18, 8.95 and 10.53 are passed. The neutral species lies between pKa 8.95 and 10.53, so pI = (8.95 + 10.53)/2 = 9.74.

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Lysine has pKa​ values 2.18 (α-COOH), 8.95 (α-NHX3​X+) and 10.53 (side-chain NHX3​X+). Taking pI as the mean of the two pKa values flanking the net-neutral species, pI is

Answer: D

More questions on Amino acids: zwitterions, isoelectric point

Lysine has $p K_{a}$ values $2.18$ ( $α$ -COOH), $8.95$ ( $α$ - $NH X_{3} X^{+}$ ) and $10.53$ (side-chain $NH X_{3} X^{+}$ ). Taking pI as the mean of the two pKa values flanking the net-neutral species, pI is