Catalysis by adsorbed enzymes. The hydrolysis of tripropionin by pancreatic lipase adsorbed to siliconized glass beads.

The reaction of porcine pancreatic lipase B (EC 3.1.1.3) with the soluble triglyceride, tripropionin, shows substantial stimulation in the presence of hydrophobic surfaces. The enhancement of the enzymatic rate can be correlated with the reversible binding of the enzyme to the hydrophobic surface with a dissociation constant K = 1.3 X 1O-8 M. The binding of the enzyme to the surface is diffusion controlled with a rate constant of 1.8 X 106 M-I ~9. At saturation of the surface with enzyme each protein molecule occupies an average area of 6000 A2 per molecule. The hydrolytic reaction on the surface is first order with respect to the amount of adsorbed enzyme and the concentration of tripropionin at the solution-solid interface. The second order rate constant of the reaction is 1.3 X 1013 cm2 mole-l s-l. The surface reaction requires a basic group on the enzyme with a pK of 5.85. The enhancement of the velocity on the surface as compared to the homogeneous reaction can be ascribed to an increased local concentration of the substrate at the liquid-solid interface.