Figure 3.

Effect of temperature on the acid dissociation constant $\text{p}{K}_1$ from plots of $\text{log}\left(k_{\text{cat }}/K_{\text{Z-RR-AMC }}\right)$ (top line) and $\text{log}{k}_{\text{cat }}$ (bottom line) vs pH. Values of $\text{p}{K}_1(n\ge 2)$ vs $1/T$ (Kelvin) were fitted to eq 12, from which $\Delta H_{\text{ion }}$ values of 8.4 ± 0.2 and $7.1\pm 0.1\text{kcal}/\text{mol}$ and a $\Delta S_{\text{ion }}$ of $0\text{cal}{\text{mol}}^{-1}{\text{K}}^{-1}$ were obtained.