PROTEINS AT THE AIR-WATER-INTERFACE AND THEIR INHIBITORY EFFECTS ON ENZYME LIPOLYSIS

The surface pressure/area dependence on pH in spread and adsorption layers of bovine serum albumin (BSA), beta-lactoglobulin A and ovalbumin was investigated by measuring the surface pressure using the Wilhelmy method. The experimentally established dependences were analyzed by means of Singer's equation as well as that established by Frisch and Simha. The deviations from the theoretical dependence can be accounted for by a partial preservation of the native protein structure. The data on the degree of unfolding of the protein molecules are compared to the adsorption activity and rheological dilatational properties. Proteins are known to be best adsorbed at the maximal unfolding of their molecules. This maximal unfolded state corresponds to small characteristic lengths of propagation of dilatational deformations along the Maxwell viscoelastic layer. The BSA, beta-lactoglobulin A and ovalbumin penetration into a dicaprin monolayer was determined by measuring the rheological dilatational properties of the mixed lipid/protein layer formed. A correlation was found between the inhibition rate (d-pi/dt)t = 0 and the rheological dilatational properties of the protein after penetrating the dicaprin monolayer. The inhibition of the lipolytic enzymatic action exerted by proteins depends on both their adsorption and penetration activity and their conformational state. The strongest inhibition of lipolysis (d-pi/dt)t = 0 = 0 was observed with BSA at pH 3. At this pH value BSA is in the maximal unfolded state and shows the highest adsorption activity.