ADSORPTION OF LIPASE TO SILICA AND METHYLATED SILICA SURFACES

The adsorption of highly purified lipase from Humicola lanuginosa at t he solid/liquid interface was monitored in situ by means of ellipsomet ry. Clean silica surfaces and silica surfaces methylated by exposure t o dichlorodimethylsilane in trichloroethylene were used. Adsorption to hydrophobic surfaces was carried out at pH 5, 7, 9, and 10.6 and the concentrations of lipase were 2.0 x 10(-3), 2.0 x 10(-2), 0.2, 1.0, an d 2.0 mg/ml. Adsorption measurements to hydrophilic surfaces were made at pH 5 and 7 at a lipase concentration of 0.2 mg/ml. In addition, th e effect of ionic strength on the adsorption was investigated, and 1:1 (NaCl) as well as 2:1 (CaCl2) electrolyte was used. The adsorption of lipase was found to be highest at pH 5 and decreased with increasing pH. The amounts adsorbed increased with increasing concentrations for measurements made at pH 7 and 9 while at pH 5, high values were reache d at the lowest concentration investigated and the concentration depen dence was less pronounced. At all pH values, it was found that the rev ersibility decreased with the concentration of the lipase. No major ef fect from the presence of NaCl was observed. The lipase adsorption was , however, substantially increased in a CaCl2 solution. (C) 1996 Acade mic Press, Inc.