AN EQUILIBRIUM AND CALORIMETRIC INVESTIGATION OF THE HYDROLYSIS OF L-TRYPTOPHAN TO (INDOLE PLUS PYRUVATE PLUS AMMONIA)

Apparent equilibrium constants and calorimetric enthalpies of reaction have been measured for the reaction L-tryptophan(aq) + H2O(l) = indole(aq) + pyruvate(aq) + ammonia(aq) which is catalyzed by L-tryptophanase. High-pressure liquid-chromatography and microcalorimetery were used to perform these measurements. The equilibrium measurements were performed as a function of pH, temperature, and ionic strength. The results have been interpreted with a chemical equilibrium model to obtain thermodynamic quantities for the reference reaction: L-tryptophan(aq) + H2O(l) = indole(aq) + pyruvate-(aq) + NH4+(aq). At T = 25-degrees-C and I(m) = 0 the results for this reaction are: K(o) = (1.05 +/- 0.13) x 10(-4), DELTA(r)G(o) = (22.71 +/- 0.33) kl-mol-1, DELTA(r)H(o) = (62.0 +/- 2.3) kJ-mol-1, and DELTA(r)S(o) = (132 +/- 8) J-K-1-mol-1. These results have been used together with thermodynamic results from the literature to calculate standard Gibbs energies of formation, standard enthalpies of formation, standard molar entropies standard molar heat capacities, and standard transformed formation properties for the substances participating in this reaction.