FIGURE 5.
pH dependence of the steady-state rate constant kss for wild-type MSDH with PPA as substrate. The pH dependence of kss was studied at 30 °C over the pH range 5.0–9.0 in buffer A. The remaining experimental conditions were as follows: 1 mm NAD, 0.05 m PPA, and 500 μm CoA. Experiments were done twice with experimental errors on the individual points ≤ 5%. Data (●) were fit by nonlinear least square regression analysis against a two-pKapp model that yielded pKapp values of 6.5 ± 0.1 and 7.8 ± 0.1, and rate constants kss(i) of 6.0 ± 0.7 s−1 and kss (max) of 18 ± 0.2 s−1, respectively (solid line). The data do not fit to a one-pKa model (dotted line).