Lysozyme is an enzyme found in (among other places) saliva that can degrade carb
ID: 1006876 • Letter: L
Question
Lysozyme is an enzyme found in (among other places) saliva that can degrade carbohydrates, including those in bacterial cell walls. The activity profile of Lysozyme with respect to pH looks like a bell curve: it rises from near 0% to almost 100% when going from pH 2 to pH 5, and drops back off to near 0% when going from pH 5 to pH 10.
The lysozyme active site contains two amino acids that appear to be important for catalysis: Glu-35 and Asp-52.
Experimental measurements suggest that the pKa values of the side chains of these two residues are 5.9 (for Glu-35) and 4.5 (for Asp-52) respectively. Which of the following statements is most likely to be TRUE? Choose the best answer.
Lysozyme activity optimally requires that both active site residues be in their deprotonated (negatively charged) formsExplanation / Answer
The correct answer is Lysozyme activity is highest when Glu-35 is protonated and Asp-52 is deprotonated.
At the pKa values [pH=5.2], which is lower pH then the pKa of Asp-52 (4.5) thus is deprotonated –COO- while GLu-35 which has higher pka (5.9) present as protonated form (-COOH)
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