The adsorption to and hydrolysis of 1,3-didecanoyl glycerol monolayers by pancreatic lipase. Effects of substrate packing density.

The kinetics of hydrolysis of 1,3-didecanoyl glycerol by pancreatic lipase were measured in monomolecular films at the air-water interface. Determination of the quantity of active enzyme associated with the film under conditions of constant reaction velocity and surface pressure showed that both the extent of enzyme adsorption and the catalytic rate constant of the adsorbed enzyme were substrate packing dependent. If this rate constant was corrected for the concentration of reactive substrate predicted from kinetic and physical studies (Momsen, W. E., and Brockman, H. L. (1979) J. Biol. Chem. 254, 8855-8860), a constant value of 2.5 +/- 0.5 X 10(12) (S.E.) cm2/(mol.s) was obtained for the second order rate constant. This constancy supports the hypothesis that a packing dependent conformational distribution of substrate head groups is a factor in the regulation of lipolysis.