Histidine is one of the 20 amino acids found in proteins. Shown here is a fully protonated histidine molecule where thenumbers denote the pKa values of the acidic groups.( pKa values: H3N+=9.17, OH=1.82, HN+=6.00)(a) Show stepwise ionization of histidine in solution (Hint: The Hion will first come off from the strongest acid group followed by the next strongest acid group and so on.)(b) A dipolar ion is one in which the species has an equal number of positive and negative charges. Identify the dipolar ion in (a).(c) The pH at which the dipolar ion predominates is called the isoelectric point, denoted by pI. The isoelectric point is the average of the pKa values leading to and following the formation of the dipolar ion. Calculate the pI of histidine.(d) The histidine group plays an important role in buffering blood. Which conjugate acid-base pair shown in (a) is responsible for this action?
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Histidine is one of the 20 amino acids found in proteins. Shown here is a fully protonated histidine molecule where the
numbers denote the pKa values of the acidic groups.( pKa values: H3N+=9.17, OH=1.82, HN+=6.00)
(a) Show stepwise ionization of histidine in solution (Hint: The Hion will first come off from the strongest acid group followed by the next strongest acid group and so on.)
(b) A dipolar ion is one in which the species has an equal number of positive and negative charges. Identify the dipolar ion in (a).
(c) The pH at which the dipolar ion predominates is called the isoelectric point, denoted by pI. The isoelectric point is the average of the pKa values leading to and following the formation of the dipolar ion. Calculate the pI of histidine.
(d) The histidine group plays an important role in buffering blood. Which conjugate acid-base pair shown in (a) is responsible for this action?
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