All amino acids have two ionizable functional groups: an alpha amino group (aver

Question

All amino acids have two ionizable functional groups: an alpha amino group (average pKa of 9.4) and an alpha carboxylic acid group (average pKa of 2.2). Histidine also has an ionizable side chain (R group) with a pKa of approximetly 6.0. At what pH would an ionized structure of Histidine be at the redominant ionization state? The protonated form of the R group of histidine is shown in the structure. The ratio of the charged (protonated) form to the deprotonated form depends on the pKa of the R group and the pH of the solution. Select the pH values at which the charged form of the R group would predominate.

Explanation / Answer

In it's isoelectric point it wiilbe redominate in ionization state i.e 9.4+6/2 =7.7

in 7.7 only the charge of side chain is redominate.

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