Variations of ammonium ion concentration and solution pH during the hydrolysis of urea by urease

Variations of product concentration and solution pH with reaction time during urea hydrolysis by urease, in both phosphate and citrate buffers, were studied. From the experimental results and the theoretical estimations based on the Michaelis‐Menten equation and the ionic equilibria of the species in solution, the inhibition behavior of urease by product and substrate was shown to be complex at high urea concentration. Furthermore, the ionic equilibria of the species in solution were significantly affected by the high concentrations of urea in the presence of buffer salts. Solution pH therefore changed to a lower value than that obtained with a lower concentration of ammonium ions. This phenomenon has not been reported and was contrary to the classic ionic equilibria. The observed results might be attributed to the character of urea and/or the more complex ionic equilibria of the species in solution.