5.

Effect of pH on the catalytic parameters for the best Kemp eliminase achieved in this work (variant V4-4) and the background protein V4. Values of catalytic rate constant and catalytic efficiency have been determined from the fitting of the Michaelis–Menten equation to profiles of rate vs substrate concentration obtained at different pH values (Figure S7). Error bars are standard deviations from the fittings of the Michaelis–Menten equation and are no not shown when they are smaller than the size of the data points. The dependence of logarithm of the catalytic rate constant with pH (left) is linear. Profiles of logarithm of catalytic efficiency vs pH are well described by eq in the main text; fittings are shown with continuous lines in panel on the right. The pK _a of the catalytic aspartic acid residue is shown. Note that the change in trend in the plot occurs at pHs close to the pK _a values (see vertical dashed lines).