1-2-oleoylphosphatidylcholine and dimyristoylphosphatidylserine

To examine the hypothesis that physical features of the membrane contribute to protein kinase C activation, phosphatidylcholine/phosphatidylserine/diolein (70:25:5) vesicles of defined acyl chain composition were tested for their ability to activate the enzyme. Maximal activation was found to correlate with the mole percent unsaturation in the system. Unsaturation could be provided by either the phosphatidylserine or the phosphatidylcholine component. Vesicles containing 5 mol% diolein but lacking any unsaturation in the phospholipid did not support activity, indicating that acidic head groups alone are not sufficient for activity. The saturated lipid vesicles could be rendered effective but only at very high (25 mol%) concentrations of diolein. The degree of acyl chain unsaturation and the positioning of the double bond had little effect on the activity, suggesting that the effect of the unsaturation is due to some physical property of the lipid rather than to a specific lipid-protein interaction. Addition of cholesterol to both saturated and unsaturated systems indicated that fluidity, as assessed by fluorescence anisotropy, did not correlate with activity. These results suggest that a physical property of the membrane other than fluidity is important for the activation of protein kinase C. A model for protein kinase C activation involving phase separation and/or head group spacing is discussed.

Topics: Animals; Brain; Diglycerides; Dimyristoylphosphatidylcholine; Enzyme Activation; Fluorescence Polarization; Liposomes; Membrane Fluidity; Phosphatidylcholines; Phosphatidylserines; Phospholipids; Protein Kinase C; Rats

Phosphatidylserine transport in normal and Rhnull red blood cells was determined by measuring characteristic morphologic changes induced by synthetic phospholipids. Treating normal A+ cells with commercial anti-A antisera, anti-Rho(D) antisera, or with saturating concentrations of purified Rho(D) antibodies had no effect on phosphatidylserine transport. Normal B- cells treated with purified anti-B antibodies transported phosphatidylserine at rates equal to those of cells not treated with antibody. Rhnull cells, deficient in the protein bearing the Rho(D) antigen, incorporated dimyristoylphosphatidylcholine and dimyristoylphosphatidylserine at rates and to extents similar to normal cells. Furthermore, incorporated phosphatidylserine, but not phosphatidylcholine, was rapidly transported across the membrane bilayer. Energy depletion or treatment with sulfhydryl reagents inhibited phosphatidylserine transport equally in normal and Rhnull cells. These results indicate that, although Rhnull cells have numerous membrane defects, they are capable of adenosine triphosphate-dependent transport of exogenously added dimyristoylphosphatidylserine. Normal phosphatidylserine transport in the presence of anti-Rho(D) antibodies or in cells deficient in the Rho(D) polypeptide indicates that this protein is not the aminophospholipid transporter.

Topics: Adult; Biological Transport; Dimyristoylphosphatidylcholine; Erythrocytes; Humans; Phosphatidylcholines; Phosphatidylserines; Phospholipases; Phospholipids; Reference Values; Rh-Hr Blood-Group System; Syndrome

We studied the interaction of transferrin receptors (of cell line Molt-4) with mixed model membranes as a function of lipid chain length (phospholipids with C14:0 and C18:1 hydrocarbon chains) and of the surface charge of the membrane using mixtures of C14:0 lecithin (DMPC) with C14:0 phosphatidylglycerol (DMPG) and C14:0 phosphatidylserine (DMPS). Spontaneous self-assembly of receptors and lipids was achieved by freeze-thaw cycles of a codispersion of mixed vesicles and receptors in buffer and subsequent separation of receptor-loaded and receptor-free vesicles by density gradient centrifugation. Information on specific lipid/protein interaction mechanisms was obtained by evaluation of protein-induced shifts of phase boundaries of lipid mixtures by calorimetry and by FTIR spectroscopy of partially deuterated lipid mixtures. The important role (1) of minimizing the elastic forces caused by the mismatch of the lengths of hydrophobic cores of the protein (lp) and the bilayer (lL) and (2) of the electrostatic coupling of protein head groups with the charged membrane/water interface for the lipid/protein self-assembly is established. The electrostatic interaction energy per receptor is about 10(3) kBT (by coupling to about 1000 charged lipids) which is sufficient to overcompensate the elastic energy associated with a mismatch of lp - lL approximately 1.0 nm. The maximum receptor concentration incorporated was measured as a function of membrane surface charge and lipid chain length. The maximum receptor molar fraction varied from xpmax = 5 x 10(-5) for DMPC to xpmax = 4 x 10(-4) for 1:1 DMPC/DMPG; moreover xpmax is higher for DMPS than for DMPG as charged component. For the long-chain lipids, xpmax is higher for a 9:1 DEPE/DEPC mixture [(4.2-9) x 10(-4)] than for pure DEPC (ca. 3.5 x 10(-4)). By decomposition of reconstituted receptors with proteases, we demonstrated the homogeneous orientation of the receptor with its extracellular head group pointing to the convex side of the vesicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Chemical Phenomena; Chemistry, Physical; Dimyristoylphosphatidylcholine; Elasticity; Freeze Fracturing; Lipid Bilayers; Liposomes; Membrane Lipids; Microscopy, Electron; Phosphatidylcholines; Phosphatidylglycerols; Phosphatidylserines; Receptors, Transferrin; Transferrin