Dipalmitoylphosphatidylcholine Bilayer Membranes Research Articles

Interaction of Poly[N-(3-aminopropyl)glycine] and Its Derivatives with Lipid Membrane

Abstract Poly[N-(3-aminopropyl)glycine] (PolyNAPGly, 5) and its derivatives were synthesized as model peptides of the membrane-bound enzymes, and investigated on their interactions with lipid membrane. PolyNAPGly (5) was shown to be distributed to dipalmitoylphosphatidyl choline bilayer membrane without destruction of the vesicle structure. Dodecyl groups were introduced to the side chains of PolyNAPGly (5), and found to facilitate binding of the polymer to lipid membrane. However, the introduction of the excess amount of hydrophobic groups to PolyNAPGly (5) caused the formation of polymer micelles, and the addition of such polymers to lipid vesicles destroyed the membrane structure. The derivative of PolyNAPGly (5) (n=35) bearing one or two dodecyl groups and some Nε-benzyloxycarbonylhistidyl groups was found to be bound tightly to lipid membrane without destruction of the membrane structure. The addition of these polypeptides to vesicles decreased the membrane fluidity.

Pyrene-labeled gangliosides: micelle formation in aqueous solution, lateral diffusion, and thermotropic behavior in phosphatidylcholine bilayers.

By use of the excimer technique, the formation in aqueous solution of pyrene-labeled ganglioside micelles and their lateral diffusion and distribution in phosphatidylcholine membranes were investigated. For these studies 12-(1-pyrenyl)dodecanoic acid was covalently attached to the ceramide part of lysogangliosides GM1, GM2, GM3, GD1a, and GD1b. The 12-(1-pyrenyl)dodecanoic acid substitute of phosphatidylcholine was used for comparison. All pyrene-labeled gangliosides were present in aqueous solution in a predominantly micellar form down to 2 X 10(-8) M, which is the technical limit of this method. The tendency to aggregate is highest for PyGD1a and PyGD1b. In fluid dipalmitoylphosphatidylcholine bilayers the excimer-to-monomer fluorescence intensity ratio of pyrene-labeled gangliosides PyGM1, PyGM2, PyGM3, PyGD1a, and PyGD1b increases linearly with ganglioside concentration. The calculated diffusion coefficients for gangliosides are comparable to 1.6 X 10(-7) cm2/s, which is the diffusion coefficient of pyrene-labeled phosphatidylcholine [Galla, H.-J., & Hartmann, W. (1980) Chem. Phys. Lipids 27, 199-219]. In comparison to phosphatidylcholine, the diffusion of monosialogangliosides is slightly increased, with that diffusion of disialogangliosides being slightly decreased. Ca2+ ions up to 200 mM do not affect ganglioside diffusion significantly. The shape of the lipid phase transition curves obtained by the excimer technique yields information on the lateral distribution of the tested probe molecules. Pyrene-labeled phosphatidylcholine was taken as reference for a system with complete miscibility but nonideal mixing. 1-Acyl-2-[10-(1-pyrenyl)decanoyl]-sn-glycero-3-phosphocholine (PyPC) is known to be randomly distributed in the gel and in the fluid-crystalline lipid phase of dipalmitoylphosphatidylcholine bilayer membranes. It distributes preferentially into the fluid phase in the phase-transition region. In comparison, PyPC in dimyristoylphosphatidylcholine membranes is an example of a system with nearly ideal mixing [Hresko, R. C., Sugar, J. P., Barenholz, Y., & Thompson, T. E. (1986) Biochemistry 25, 3813-3828]. Phase-transition curves of pyrene-labeled gangliosides exemplify a nearly ideal mixing system with PyGD1a or PyGD1b producing best effects. The monosialogangliosides, however, exhibit less ideality of mixing, the deviation from an ideal mixing behavior increasing with decreasing number of both neutral sugar residues and sialic acid groups. Addition of Ca2+ triggers a tightening of the phosphatidylcholine bilayer and thus induces a change in the lateral distribution of the gangliosides at the phase transition.(ABSTRACT TRUNCATED AT 400 WORDS)

Thermodynamic characterization of interactions between ornithine transcarbamylase leader peptide and phospholipid bilayer membranes.

The interactions of the targeting sequence of the mitochondrial enzyme ornithine transcarbamylase with phospholipid bilayers of different molecular compositions have been studied by high-sensitivity heating and cooling differential scanning calorimetry, high-sensitivity isothermal titration calorimetry, fluorescence spectroscopy, and electron microscopy. These studies indicate that the leader peptide interacts strongly with dipalmitoylphosphatidylcholine (DPPC) bilayer membranes containing small mole percents of the anionic phospholipids dipalmitoylphosphatidylglycerol (DPPG) or brain phosphatidylserine (brain PS) but not with pure phosphatidylcholines. For the first time, the energetics of the leader peptide-membrane interaction have been measured directly by using calorimetric techniques. At 20 degrees C, the association of the peptide with the membrane is exothermic and characterized by an association constant of 2.3 X 10(6) M-1 in the case of phosphatidylglycerol-containing and 0.35 X 10(6) M-1 in the case of phosphatidylserine-containing phospholipid bilayers. In both cases, the enthalpy of association is -60 kcal/mol of peptide. Additional experiments using fluorescence techniques suggest that the peptide does not penetrate deeply into the hydrophobic core of the membrane. The addition of the leader peptide to DPPC/DPPG (5:1) or DPPC/brain PS (5:1) small sonicated vesicles results in vesicle fusion. The fusion process is dependent on peptide concentration and is maximal at the phase transition temperature of the vesicles and minimal at temperatures below the phase transition.

Ultrasonic studies of membrane suspensions

The mechanical and the dynamic properties of various membranes were studied by the ultrasonic-resonance method. The compressibility of the membranes was in the range from 2.5·10−11 to 5·10−11 cm2/dyn and influenced by several factors such as phase transition, incorporation of cholesterol or proteins and configuration of proteins. The ultrasonic relaxation was measured for two membrane systems, dipalmitoylphosphatidylcholine bilayer and sarcoplasmic-reticulum membrane. The results indicated that the ultrasonic measurements are very sensitive to the co-operative transition in lipid bilayers as well as the relaxation of biological membranes containing intrinsic proteins.

Anomaly of transport of dipicrylamine anions across the central barrier of planar dipalmitoylphosphatidylcholine bilayer membranes at the phase transition

The rate of translocation of the hydrophobic ion dipicrylamine across planar lipid membranes formed from dipalmitoyllecithin in n-decane was determined by voltage jump relaxation experiments. The activation energy of the rate constant shows a change from a positive to a negative value at about 42°C near the main phase transition temperature of this lipid. Below this temperature, the rate constant was found to increase with decreasing temperature. This anomalous behaviour extends over a temperature range of at least 10 K and may be formally interpreted as an enhanced mobility of dipicrylamine in the solid state of the membrane.