Kinetics parameters of acylphosphatases with and without the active-site salt-bridge.

Values of the free energy (ΔG#), enthalpy (ΔH#), and entropy (ΔS#) of activation at 298 K were calculated by ΔG# = RT(lnkBT / h − lnkcat), ΔH# = Ea − RT , and TΔS# = ΔH# − ΔG#, where kB is the Boltzmann constant, h is the Planck constant, and R is the universal gas constant. ΔΔG#, ΔΔH#, and ΔΔS# represent the changes of these thermodynamic parameters upon the removal of the salt-bridge between the active-site arginine residue and the C-terminal carboxyl group. For comparison, at 298 K, ΔG#, ΔH#, and TΔS# of the uncatalyzed hydrolysis of benzoyl phosphate are 100.8, 102.2, and 1.4 kJ mol−1, respectively [12]. The Km values were 0.10±0.03 mM for all acylphosphatases in temperature range studied.