(747f) Thermodynamic Studies of Enzyme-Catalyzed Reactions

The combination of equilibrium measurements, microcalorimetry, and equilibrium modeling allows for the characterization of the thermodynamic properties of biochemical reactions. Both the equilibrium and calorimetry measurements yield, respectively, values for apparent equilibrium constants K' and molar calorimetric enthalpies of reaction Δ_rH(cal) for overall biochemical reactions that involve sums of species. This is a different situation than with the usually encountered reactions where only specific species participate in a reaction. Because of this, the values for K' and Δ_rH(cal) vary with pH and pMg (pMg = ‑log₁₀[Mg²⁺]), and, of course, temperature. These variations can be calculated by using an equilibrium model. The equilibrium model also leads to values of the equilibrium constant K and standard molar enthalpy of reaction Δ_rH° for a (reference) reaction that involves specific species. The aforementioned combination of tools has been applied to a large number of enzyme-catalyzed reactions, many of which are of significant interest to biotechnology and biomanufacturing. The methods will be described along with selected applications involving important biochemical reactions. The extant literature in this area has been examined and summarized in the form of several published reviews (see J. Phys. Chem. Ref. Data (2007) 36, 1347-1397 and references cited therein) and is also available as an on-line database: https://randr.nist.gov/enzyme/Default.aspx