Kinetic Constant: kcat_ex/Keff_S
Catalytic efficiency (kcat/Km)
kcat_ex is the rate constant for maximal conversion between substrate and product while Keff_S is the effective binding constant of the substrate ([S] is the concentration of either CO2 or HCO3− depending on the direction of the reaction). The ratio expressed as kcat_ex/Keff_S is in principle the same as kcat/Km obtained under steady-state conditions.
Enzyme activity was measured while increasing amounts of urea up to 8 M in 1 M increments. The solutions contained urea, 25 mM of all species of CO2 and 100 mM 4-(2-hydroxyehtyl)-1-piper-azineethane sulfonic acid (HEPES) at pH 7.6 and 25°C. An enzyme was added to the reaction vessel and catalytic O18 exchange activity was measured as R1/[E] over a period of up to 5 min.