ACTIVITY AND ADSORPTION OF LIPASE FROM HUMICOLA-LANUGINOSA ON SURFACES WITH DIFFERENT WETTABILITIES

The adsorption of Humicola lanuginosa lipase and the activity of the a dsorbed lipase were studied as a function of surface wettability. The adsorption was measured by in situ ellipsometry, and the surfaces used were methylated silica surfaces. The activity of the adsorbed lipase was measured after rinsing of the cuvette, i.e., with no lipase in the bulk: solution, in situ by the hydrolysis of p-nitrophenyl acetate. T he lipase adsorption and activity measurements were made at concentrat ions of the lipase in the range 63-1050 nM, and from the surface conce ntrations the specific activity was calculated. The study was carried out using fully methylated surfaces (hydrophobic; 90 degrees water con tact angle) and surfaces with a higher wettability (80 degrees, 75 deg rees, and 62 degrees water contact angle). All experiments were perfor med in 3-(N-morpholino)propanesulphonic acid (MOPS) buffer at pH 7.5. The adsorbed amount was found to be highest at lipase concentrations i n the range 200-300 nM and decreased with increasing wettability of th e surfaces. The fraction desorbable upon dilution of the adsorbed lipa se was found to decrease with the concentration. The specific activity of the lipase was found to increase with increasing wettability of th e surface, probably due to changes in the orientation/conformation of the adsorbed lipase. Additional experiments were performed where lipas e was adorbed to surfaces with a water contact angle of 90 degrees, in the presence of 0.03 M CaCl2. The lipase concentrations were then 63 and 1050 nM. The amount adsorbed was significantly increased in the pr esence of CaCl2, but no value for the specific activity of the adsorbe d lipase could be calculated due to the high activity originating from lipase adsorbed to the background surfaces (cuvette walls, Teflon tub ing, and magnetic stirrer).