Kinetic Study of Enzymatic Urea Hydrolysis in the pH Range 4–9

The enzymatic hydrolysis of urea by jack bean urease was investigated at 25 °C over the pH range 4–9. Reaction rate data were found to be well described by a modified Michaelis-Menten equation with a pH-dependent rate coefficient and a product inhibition term. The influence of pH on activity was interpreted in terms of perturbation of the enzyme distribution among three differently protonated forms. Kinetic analysis yielded a Michaelis constant of 3.21 mmol l and indicated that the inhibition mechanism was of the fully non-competitive type, with K P = 12.2 mmol l. The estimated activation energy was 35.3 kJ mol. The resulting kinetic expression was tested by comparing model predictions with the experimental behaviour observed in unbuffered media and over a long-term period.