Activity and stability of jack bean urease in the presence of peat humic acids obtained using different extractants

The effects of two humic acid extractants, 0.1M Na4P2O7 plus 0.1M NaOH (NaP P) and 0.1M NaOH (NaOH), on the activity and stability of a humic-urease co mplex were studied. The two humic acids isolated (HA(NaPP) and HA(NaOH)) ex hibited different elemental compositions, metal concentrations and structur al modifications in the FT-IR spectra. Depending on the pH, HA(NaPP) and HA (NaOH) influenced both the urease activity and urease kinetic parameters (V -max and K-m) in the same way. They inhibited urease activity between pH 6 and 7 and reduced the V-max of the reaction at pH 6 and 7. The presence of humic acids improved the affinity of the enzyme for the substrate (K-m). Th e stability of the urease with time, and in the presence of pronase, was im proved by HA(NaPP) and HA(NaOH) With respect to free enzyme. These results confirm the importance of the interaction of urease with humic acids as a f undamental gateway for extracellular urease stabilisation. Since no differe nce in the extent of urease inhibition and urease stabilisation was observe d for the two humic acids, it may be concluded that neither urease activity nor stability are influenced by the humic acid extractant used.