Name:

Kinetic Constant: kcat_ex/Keff_S

Category:

Activity

Property:

Catalytic efficiency (kcat/Km)

Units:

1/(s·µM)

Measurement Technique:

O18-Exchange Method

Buffers:

None

Temperature:

25 °C

pH:

7.6

Protein Concentration:

None

Wavelength:

None

Ionic Strength:

None

Details:

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.