Suppose that an enzyme uses a catalytic mechanism in which a functional group on the enzyme has to accept a proton from the intermediate formed in the first chemical step. The pKa of that basic functional group on the enzyme is 8.0, and is the only pKa apparent on a plot of kcat vs. pH for the activity of this enzyme. The kcat of the fully active form of the enzyme is 1 x 105 sec–1 .
1. Calculate the fraction of the total enzyme active sites in solution that would be in the active form at pH 7.2.
2. Calculate what kcat would be if the activity of the enzyme were measured at pH 7.2.