Recommendations for performing measurements of apparent equilibrium constants of enzyme-catalyzed reactions and for reporting the results of these measurements.

The measurement of values of apparent equilibrium constants ' for enzyme-catalyzed reactions involve a substantial number of critical details, neglect of which could lead to systematic errors. Here, interferences, impurities in the substances used, and failure to achieve equilibrium are matters of substantial consequence. Careful reporting of results is of great importance if the results are to have archival value.

Recommendations for terminology and databases for biochemical thermodynamics.

Chemical equations are normally written in terms of specific ionic and elemental species and balance atoms of elements and electric charge. However, in a biochemical context it is usually better to write them with ionic reactants expressed as totals of species in equilibrium with each other. This implies that atoms of elements assumed to be at fixed concentrations, such as hydrogen at a specified pH, should not be balanced in a biochemical equation used for thermodynamic analysis.

Thermodynamics of the hydrolysis reactions of 1-naphthyl acetate, 4-nitrophenyl acetate, and 4-nitrophenyl α-L-arabinofuranoside.

Microcalorimetry, high-performance liquid chromatography (HPLC), and liquid chromatography-mass spectrometry (LC-MS) have been used to conduct a thermodynamic investigation of the hydrolysis reactions {1-naphthyl acetate(aq) + H(2)O(l) = 1-naphthol(aq) + acetate(aq)}, {4-nitrophenyl acetate(aq) + H(2)O(l) = 4-nitrophenol(aq) + acetate(aq)}, and {4-nitrophenyl α-L-arabinofuranoside(aq) + H(2)O(l) = L-arabinose(aq) + 4-nitrophenol(aq)}. Calorimetrically determined enthalpies of reaction Δ(r)H(cal) were measured for all three reactions. However, since the positions of equilibrium for all of these reactions were found to lie very far to the right, it was only possible to set lower limits for the values of the apparent equilibrium constants K'.

Thermodynamics of enzyme-catalyzed reactions--a database for quantitative biochemistry.

Unlabelled: The Thermodynamics of Enzyme-catalyzed Reactions Database (TECRDB) is a comprehensive collection of thermodynamic data on enzyme-catalyzed reactions. The data, which consist of apparent equilibrium constants and calorimetrically determined molar enthalpies of reaction, are the primary experimental results obtained from thermodynamic studies of biochemical reactions. The results from approximately 1000 published papers containing data on approximately 400 different enzyme-catalyzed reactions constitute the essential information in the database.

Thermodynamics of reactions catalyzed by PABA synthase.

Microcalorimetry and high-performance liquid chromatography (HPLC) have been used to conduct a thermodynamic investigation of reactions catalyzed by PABA synthase, the enzyme located at the first step in the shikimic acid metabolic pathway leading from chorismate to 4-aminobenzoate (PABA). The overall biochemical reaction catalyzed by the PabB and PabC components of PABA synthase is: chorismate(aq)+ammonia(aq)=4-aminobenzoate(aq)+pyruvate(aq)+H(2)O(l). This reaction can be divided into two partial reactions involving the intermediate 4-amino-4-deoxychorismate (ADC): chorismate(aq)+ammonia(aq)=ADC(aq)+H(2)O(l) and ADC(aq)=4-aminobenzoate(aq)+pyruvate(aq).

An Equilibrium Model for the Calculation of Activity and Osmotic Coefficients in Aqueous Solutions.

A procedure is described for the calculation of activity and osmotic coefficients which is based upon a knowledge of the equilibria in solution and assumed single-ion activity coefficients. The procedure permits one to introduce chemical equilibria of various types (ion-pairing, complexation, hydration, and hydrolysis) into a model which can be used to calculate values of the excess Gibbs energy and the activity and osmotic coefficients. Both the Debye-Hückel theory and Pitzer's expression are used to calculate the electrostatic contribution to the single-ion activity coefficients.

The Enthalpy of Reaction of Tris(hydroxymethyl)aminomethane With Hydrochloric Acid.

The enthalpy of reaction of tris(hydroxymethyl)aminomethane with 0.1 HCl has been measured using an isoperibol solution calorimeter, employing a modified quartz thermometer and an automatic digital data acquisition system. The enthalpy value obtained at 298.