Adsorption, Desorption And Activities Of Acid Phosphatase On Various Active Particles From A Permanent-charge Soil

Organic and inorganic Coarse colloid (0.2-2μm) and fine colloid (<0.2μm) were separated from a Brown soil collected from Taishan, Shandong Province. Adsorption characteristics of acid phosphatase on these soil colloids were investigated. Desorption by phosphate buffer, Tris-HCL buffer and NaCl solution of bound enzymes was also studied.Effect of temperature and pH on the enzymatic activity of acid phosphatase on various soil colloids was also investigated. The main results are outlined as follows.1. The content of organic matter for test soil colloids ranged from 5.9 to 74.4 g · kg^-1. The specific surface area was from 31.7 to 116.5 m² · g^-1 for test soil colloids. Fine soil colloids have larger CEC values than the coarse soil colloids. Fine soil colloids contain higher amounts of illite than the corresponding coarse soil colloids.2. The adsorption isotherm of acid phosphatase on test soil colloids conformed to the Langmuir equation (r>0.96). Greater amounts of enzyme were adsorbed by fine soil colloid than by coarse soil colloid. Organic soil colloid adsorbed more enzymes than inorganic soil colloid. Adsorption was enhanced by the presence of organic matter in soil colloids.3. Temperature affected more significantly on the adsorption of enzymes by coarse soil colloids and inorganic soil colloids. Adsorption of enzyme on soil colloids increased with pH from 4.0-5.0 and decreased with pH from5.0-9.0. Higher amounts of adsorption were observed at pH 4.0-5.0 than at pH 5.0-9.0.4.More enzymes were desorbed from coarse soil colloids than from fine soil colloids. The percent desorption of enzyme from organic soil colloids was grater than inorganicsoil colloids. Enzymes immobilized on coarse soil colloids and organic soil colloids were desorbed more easily.5. The specific activities of acid phosphatase immobilized on soil colloids ranged from 54.2% to 81.1%. The optimal temperature of acid phosphatase adsorbed on test soil colloids was 35°C which is the same as that of free enzyme. The specific activities and thermal stabilities of acid phosphatase immobilized on organic soil colloids were higher than those on inorganic soil coiloids.The activity of enzyme was inhibited more considerably than on coarse soil colloid than that on fine colloids. The enzyme on coarse colloid was more resistant to thermal deactivation.6. The specific activities of acid phosphatase immobilized on test soil colloids was maximum at pH 5.0 and decreased steadily at pH > 5.0 and at pH < 5.0. Immobilized acid phosphates immobilized by test soil colloids showed similar pH-activity profiles as that of free enzyme.