ESR center line shifts during phase transitions of spin-labeled dipalmitoyl phosphatidyl choline and dipalmitoyl phosphatidyl ethanolamine

The position H_o of the ESR central absorption maximum of a spin-labeled phospholipid dispersion was recorded in the manner of a g-factor; γ=hν/βH_o. The point H_o corresponds to the center line zero crossing point of the first derivative ESR spectrum. A 5-doxyl derivative of stearic acid was incorporated into dispersions of dipalmitoyl phosphatidyl choline and dipalmitoyl phosphatidyl ethanolamine formed either by shaking a lipid film in the presence of buffered saline or by dialysis of label and lipid in 2-chloroethanol against buffered saline. It was found that during the gel to liquid crystal phase transition, the decrease in the order parameter, S, ranged from about .045 to .06 and the increase in the parameter γ ranged from about .0001 to .0002 depending upon the lipid and preparation method. In all cases examined, the changes could be associated with the lipid phase transition. A simple model based on rapid anisotropic motion indicates that about a 38% decrease in line width accounts for the observed shift in γ.     

Immunochemical properties of phosphatidyl cholesterol and its homologue

1,2-Dipalmitoyl-rac-glycerol-3-phosphoryl-3'-cholesterol (PCH) and 1,2-dipalmitoyl-rac-glycerol-3-phosphoryl-20'-(3-hydroxy norpregn-5-ene) (PET) were combined with poly-L-lysine to form a PCH-poly-L-lysine complex and a PET-poly-L-lysine complex, respectively. These complexes were subcutaneously injected into rabbit foot pad with Freund's complete adjuvant. PCH antiserum showed specificites against the phosphatidyl group, the cholesterol moiety and the side chain of cholesterol. PET antiserum contained the specific antibodies against the phosphatidyl group, the cholesterol moiety and the OH-group at the C3 position of the cholesterol molecule.     

Phorbol myristate acetate stimulates formation of phosphatidyl inositol 4-phosphate and phosphatidyl inositol 4,5-bisphosphate in human platelets

There are conflicting data in the literature as to whether or not the Ca2+ activation of phospholipase A2 is mediated by the calcium binding protein calmodulin. In the present study the membrane-bound phospholipase A2 enzymes in rat and human platelets were shown to be absolutely Ca2+ dependent but were not stimulated by the addition of calmodulin. A partially purified phospholipase A2 from rat platelet membrane, which contained little endogenous calmodulin, also was not stimulated by calmodulin addition. Both isolated and membrane-bound phospholipase A2 were inhibited by the non-specific calmodulin antagonist trifluoperazine but the inhibition was not overcome by adding calmodulin. There was thus no evidence from these studies that phospholipase A2 is calmodulin regulated.     

A simplified preparation of phosphatidyl inositol

A method is described for the rapid isolation of phosphatidyl inositol from soybean phosphatides (Asolectin). The product is obtained pure as the crystalline sodium salt.     

Preferential interaction of dimethyl sulfoxide and phosphatidyl choline membranes

The interaction free energy of dimethyl sulfoxide (DMSO) and two types phospholipid membranes has been assessed from measurements of vapor pressure. The lipids were phosphatidyl cholines with respectively (14:0/14:0) (DMPC) and (16:0/18:1) (POPC) fatty acid chains. The results were expressed in terms of the iso-osmolal preferential interaction parameter, Γ_μ1, which remained negative under all experimental conditions investigated here. This shows that water-membrane interactions are more favorable than DMSO-membrane interactions. This condition is known as preferential exclusion of DMSO (or preferential hydration of the membrane), and implies that the local (interfacial) concentration of the solute is reduced compared to the bulk. At room temperature and 1 m DMSO, Γ_μ1 was −0.3 to −0.4 for both lipids. This corresponds to a sizable reduction in the DMSO concentration in a zone including at least the first two hydration layers of the membrane. Possible origins of the preferential exclusion are discussed.As a direct consequence of the pronounced preferential exclusion, DMSO generates an osmotic stress at the membrane interface. This tends to stabilize lipid phases of low surface areas and to withdraw water from multilamellar stacks of membranes. Based on this, we suggest that the preferential exclusion of DMSO explains both the modulation of phase behavior and the constriction of multilamellar aggregates induced by this solute.     

Preferential interaction of dimethyl sulfoxide and phosphatidyl choline membranes

The interaction free energy of dimethyl sulfoxide (DMSO) and two types phospholipid membranes has been assessed from measurements of vapor pressure. The lipids were phosphatidyl cholines with respectively (14:0/14:0) (DMPC) and (16:0/18:1) (POPC) fatty acid chains. The results were expressed in terms of the iso-osmolal preferential interaction parameter, Gamma(mu1), which remained negative under all experimental conditions investigated here. This shows that water-membrane interactions are more favorable than DMSO-membrane interactions. This condition is known as preferential exclusion of DMSO (or preferential hydration of the membrane), and implies that the local (interfacial) concentration of the solute is reduced compared to the bulk. At room temperature and 1 m DMSO, Gamma(mu1) was -0.3 to -0.4 for both lipids. This corresponds to a sizable reduction in the DMSO concentration in a zone including at least the first two hydration layers of the membrane. Possible origins of the preferential exclusion are discussed. As a direct consequence of the pronounced preferential exclusion, DMSO generates an osmotic stress at the membrane interface. This tends to stabilize lipid phases of low surface areas and to withdraw water from multilamellar stacks of membranes. Based on this, we suggest that the preferential exclusion of DMSO explains both the modulation of phase behavior and the constriction of multilamellar aggregates induced by this solute.     

Biosynthesis of phosphatidyl glycerophosphate in Escherichia coli

An enzyme (L-glycerol 3-phosphate: CMP phosphatidyltransferase) catalyzing the synthesis of phosphatidyl glycerophosphate from CDP-diglyceride and L-glycerol 3-phosphate has been rendered soluble by treatment of the particulate, membrane-containing fraction of E. coli with Triton X-100 and has been partially purified. The enzyme, devoid of phosphatidyl glycerophosphatase activity, is specific for L-glycerol 3-phosphate and is completely dependent upon added Mg(++) or Mn(++) for activity. It has high affinity for CDP-diglyceride and can be used for the assay of this nucleotide. Other properties of the enzyme are also described.