INTERACTIONS OF SATURATED DIACYLGLYCEROLS WITH PHOSPHATIDYLCHOLINE BILAYERS - A H-2 NMR-STUDY

The interactions of a series of saturated diacylglycerols (DAGs) with fatty acid side chain lengths of 6-14 carbons with multilamellar phospholipid bilayers consisting either of dipalmitoylphosphatidylcholine (DPPC) or of a mixture of DPPC and bovine liver phosphatidylcholine (BL-PC) extracts were studied by H-2 NMR spectrometry. We found that the perturbation induced by the DAGs into the bilayer structure strongly depends on the length of the DAG fatty acid side chain. Shorter chain 1,2-sn-dihexanoylglycerol and, to a larger degree, 1,2-sn-dioctanoylglycerol (diC8) induce transverse perturbation of the bilayer structure: the order parameters of the phospholipid side chains are increased by the intercalating DAG molecules in the region adjacent to the phospholipid headgroups and decreased toward the terminal methyls, corresponding to the bilayer interior. The longer chain DAGs (C greater-than-or-equal-to 12) studied in this and previous [De Boeck & Zidovetzki (I 989) Biochemistry 28, 7439] work induce lateral phase separation of the lipids into DAG-enriched gellike domains and relatively DAG-free regions in the liquid-crystalline phase. Each of the DAGs studied induces a decrease in the area per phospholipid molecule, and a corresponding increase in the lateral surface pressure of the bilayers. Since numerous biochemical studies consistently report that diC8 is the most effective of saturated DAGs in activating protein kinase C, we may conclude that the activation of this enzyme is associated with a transverse perturbation of the lipid bilayer structure and a decreased ordering in the interior of the bilayer membrane, and is less affected by the lateral phase separation of the lipids into regions of different fluidities, as induced by the longer chain DAGs. The DAG-induced lateral phase separation may, however, play a role in activating other enzymes, such as pig pancreatic phospholipase A2.