Thermodynamics of the reduction of NADP with 2-propanol catalyzed by an NADP-dependent alcohol dehydrogenase

The apparent equilibrium constant of the biochemical reaction, 2-propanol + NADPox=acetone + NADPred, was determined at I=0.25 M over a wide range of pH (5.63 to 8.02) and temperature (5 to 40 °C). The reaction was catalyzed by an NADP-dependent alcohol dehydrogenase. The results were used to calculate thermodynamic quantities for the chemical (ionic) reference reaction: 2-propanol + NADPox3−=acetone + NADPred4−+H+. The thermodynamic quantities for this reference reaction are as follows: equilibrium constant K=(5.98±0.46)×10−10; standard molar Gibbs energy change ΔrG0=(52.65±0.19) kJ mol−1; standard molar enthalpy change ΔrH0=(38.9±0.6) kJ mol−1; and standard molar entropy change ΔrS0=−(46.1±2.2)J K−1 mol−1. All of these results pertain to 25 °C (298.15 K) and I=0. The results also lead, in conjunction with tabulated thermodynamic quantities, to the standard electromotive force E0=−0.140 V for the reduction of NADPox3− to NADPred4−.