Which of the following amino acid residues would you most ex

Which of the following amino acid residues would you most expect to be important at the active site of an enzyme?

12) Which of the following amino acid residues would you most expect to be important at the active site of an enzyme? H3C OH OH OH HO NH, NH NH NH HN NH2

Solution

Answer : The correct answer is C. The amino acid depicted in the C is the Histidine. It has an imidazole group. Histidine is the only common amino acid having an ionizable side chain with a pKa near neutrality. In many enzyme-catalyzed reactions, a His residue facilitates the reaction by serving as a proton donor/acceptor.