Calculation of specificity constants Γ for RUBISCO of different species from microcalorimetric data

Based on earlier data concerning the reaction enthalpy [Formula: see text] of Ribulose 1,5-bisphosphate carboxylase/oxygenase (RUBISCO) from spinach (Frank et al. Phys Chem Chem Phys 2:1301-1304, 2000), it is shown that the specificity constant [Formula: see text], indicating the ability of RUBISCO to discriminate between CO₂ and O₂ as substrate, can be determined from an isothermal titration calorimetric (ITC) measurement of [Formula: see text] as a function of the substrate concentration ratio [Formula: see text]. The approach does not need any radioactive materials and might be a cost-effective alternative for RUBISCO engineering to screen for variants with a high specificity constant.