Aspartate and Lysine Are in the Active Site of an Enzyme

Aspartate and lysine are in the active site of an enzyme. They are both known to participate directly in catalysis. The pK_aʹs of the residues are found to be 3.2 and 9.6, respectively for aspartate and lysine. The optimum pH for the enzyme is 6.4. Which forms of these two residues will predominate when the enzyme is most active?

A) aspartate is protonated; lysine is deprotonated
B) both residues are protonated
C) aspartate is deprotonated; lysine is protonated
D) both residues are deprotonated