Lipoprotein lipase-catalyzed hydrolysis of dimyristoylphosphatidylcholine. Effect of lipid organization and apolipoprotein C-II on enzyme activity.

The effect of phospholipid organization on the lipoprotein lipase-catalyzed hydrolysis of dimyristoylphosphatidylcholine was examined with sonicated vesicles and Triton X-100 or lysomyristoylphosphatidylcholine solubilized lipid. Triton X-100-dimyristoylphosphatidylcholine substrates were prepared at various ratios of detergent to phospholipid so as to produce lipid structures varying from bilayers to micelles. Apolipoprotein C-II, the activator protein for lipoprotein lipase, enhanced the rate of the lipoprotein lipase-catalyzed hydrolysis of dimyristoylphosphatidylcholine for each substrate tested. Although the absolute rate of lipoprotein lipase catalysis was different for each, the factor (the ratio of lipoprotein lipase activity with apolipoprotein C-II to that without the activator protein) was nearly constant, with a value of approximately 16. We conclude that the enhancement of lipoprotein lipase activity by apolipoprotein C-II is independent of the physical form of the phospholipid substrate.