Lipoprotein lipase-catalyzed hydrolysis of phospholipid monolayers: effect of fatty acyl composition on enzyme activity.

The phospholipase A1 activity of lipoprotein lipase (LpL) was determined with monomolecular phospholipid films. Rates of phospholipid hydrolysis were dependent on apolipoprotein C-II (the activator protein for LpL) phospholipid fatty acyl composition, and lipid-packing density. In sphingomyelin: cholesterol (2:1, molar) monolayers containing 5 mol % disaturated phosphatidylcholines (PC) and at a surface pressure of 22 mNm-1, rates of LpL hydrolysis of diC14:0PC, diC16:0PC, and diC18:0PC were 74, 207, and 65 nmol h-1 mg LpL-1, respectively. At 22 mNm-1, phospholipids containing unsaturated fatty acyl chains were hydrolyzed at rates 5-10 times greater than saturated lipids. At higher lipid packing densities, the difference in hydrolysis rates between saturated and unsaturated lipids was less apparent. Comparison of molecular areas indicate no simple dependency between the rate of LpL catalysis and phospholipid fatty acyl chain length and saturation/unsaturation.