Influence Of Soil Humic Acid On The Activity And Stability Of Urease

In this paper we studied the activity of urease binding with humic acid (HA) at differernt pH, ionic concentration with and without copper, and the stability of humic acid-urease complex with time. The properties of humic acid were measured by using fourier infrared spectrum, transmission electron microscope and fluorescence spectrum. The main results are outlined as follows:1. The activity of urease-HA complex decreased with the increase of humic acid concentration. But the falling degree was different at different pH value. At pH4.0, the activity of urease dropped rapidly to 0 after the addition of the humic acid (mass ratio≥0.1). And at pH5.0, the activity of complex was between 0.5% and 1.5% after f=0.4. However, the urease still maintained high activity around 93.0% after binding with humic acid at pH7.0 and FA had little effect on the its activity at the same pH value; With the increasing of pH value, the activity of the complex keep going up. At pH8.0, the activity of urease with humic acid can attain 113.1%. Humic acid can protect the urease activity, because of the competition between humic acid and substrate for bindig with urease molecular.2. Salt concentration had opposite effect on the complex activity at different pH. At 0.05M KC1 concentration, HA had little effect on urease activity, but FA can improve its activity by 3.0%-8.14% at pH5.0. However, at pH7.0 the activity of urease can be inhibited by Humic acid there was an upward trend following with an downward trend.3. The activities of free urease and complex were falling down with time at pH7.0 and 8.0. Especially, the protection of urease by JGHA was more obvious. At pH7.0, the activity of urease with humic acid dropped to 0 at the 12th day, and the falling rate became slower at higher mass ratio (f). For urease-FA, at the 12th day and f≥0.8, the activity remained 16.9%; At pH 8, the activity of urease with HA enhanced with the increase of mass ratio, the activity was about 59% when f=1.0. For urease-FA, its activity was similar to that at pH7.0.4. Humic acid can protect the urease molecular from the interaction with copper. By increasing the concentration of humic acid, the urease activity increased gradually. The activity was higher when copper was add to the complex of urease-HA than that when urease, HA and copper were mixed at the same time. When the mass of humic acid was increased, the activity of HA-urease with Cu2+ went up slowly.5. The fluorescence intensity of tyrosine and tryptophan was higher in pH=7.0 than that of other condition used by Sychronous fluorescence spectrum. By increasing the mass ratio, the fluorescence intensity of Urease-HA complex reduced. The fluorescence intensity was nearly 0 when mass ratio (f) was 1.0.