DMPC vesicles

Monnard and Deamer (2001) carried out further studies, using DMPC liposomes, to determine their properties under conditions of passive diffusion of dissolved molecules. The passage across the lipid bilayer is a precondition for the intake of nutrient substances via the vesicle envelope. The experiments showed that even polar molecules can enter the interior of the liposomes oligonucleotides, however, cannot cross the lipid bilayer of DMPC vesicles. 

Aggregation of pseudoisocyanine (dye I, Fig. 3) and 5,5 -dichloro-3,3 -diethyl-9-phenylthiacarbocyanine chloride (dye II, Fig. 5) induced by the vesicles consisting of zwitterionic DMPC and anionic DCP (Fig. 6) lipids was studied in [28]. Both dyes were shown to form fluorescent J-aggregates upon addition of the vesicles formed of the mixture of DMPC and DCP with relative content equal to 1 1. At the same time, for both dyes pure DMPC vesicles did not induce the J-aggregation. Upon addition of the vesicles containing DMPC and DCP in the 4 1 ratio, as well as... 

Fig.4 3ip -NMR spectra of phospholipids reconstituted with GS, showing A the same oriented sample as in Fig. 2A (1 20), and B dispersion of unilamellar DMPC vesicles in excess buffer containing gramicidin S in a 1 10 peptide lipid ratio...

Fig. 6. The intensity of the (CH2) /CH3 cross-peaks in sonicated DMPC vesicles (0.09 M) at different pressures from 1 bar to 2000 bar as a function of the mixing time (r=64°C) (after Ref. 19).

Fig. 8. H, H NOESY spectra (stagged and contour plot) of sonicated DMPC vesicles at 700 bar (left) and 2000 bar (right) for r= 64 °C (t = 800 ms).

Experimental demonstration that the enzyme inside dimyristoylphosphatidylcholine (DMPC) vesicles was active against externally added ADP, yielding lipid vesicle trapped poly (A). 

Table II gives the ratios of the 31P-NMR linewidths in the presence of calcium or magnesium for egg PC and DMPC vesicles. For egg PC this ratio is 1.0 at 10° and 20°C, indicating that calcium and magnesium have identical dissociation constants in their binding to egg PC at these temperatures. At 35°C the ratio is slightly less than 1.0. This difference, however, is small compared with the effects observed with saturated phosphatidylcholines.

For DMPC vesicles at 35°C, the ratio of 31P-NMR linewidths in the presence of calcium or magnesium is substantially less than 1 (0.82). This indicates that calcium binds more tightly than magnesium to DMPC. At 10° C, the linewidth ratio is further reduced (0.75), indicating that the selectivity of DMPC for calcium over magnesium is enhanced below the phase transition (Tc 22°C for sonicated vesicles (12)). Very similar results were obtained with DPPC vesicles. 

The effect of organophosphorous insecticides such as methylbromfenvinfos on membrane fluidity has been studied using the fluorescence anisotropy of 1,6-diphenyl-l,3,5-hexatriene (DPH), a probe known to be located in the hydrophobic core of the bilayer, and 1,3-bis (1-pyrene) propane (Py(3)Py), a probe distributed in the outer layer region [54]. DPH revealed a broadening of the transition profile and a solidifying effect in the fluid phase of DMPC and DPPC in the presence of 50 pM insecticide. An ordering effect of the insecticide in the fluid state was revealed by Py(3)Py. In addition, the pretransition in DPPC and DMPC vesicles was abolished by the insecticide. The addition of cholesterol decreased the influence of the insecticide. It was also observed that the influence on native membranes (erythrocytes, lymphocytes, brain microsomes, and sarcoplasmic reticulum) depended on the cholesterol content of the membranes. 

This method is illustrated in Fig. 15 for the simulated spectra for the AA B type spectrum for C26 and C27 of 16.67 mol% [25,26,27-13C]cholesterol in dimyristoylphosphatidyl choline (DMPC) vesicles at 90 MHz. The simulated spectrum is plotted using 100 data points, where 1% noise (i.e. SNR of 100) has been added. The solid line represents the fitted lineshape. The parameters obtained from the fit are compared with their known values in Table 4. Since each component in the spectrum corresponds to a quadratic factor of the denominator polynomial (cf. Eq. (84)), estimates of the position and width of a line may be determined from the real and imaginary parts, respectively, of the appropriate zeros of the denominator polynomials (a iflk,k= 1,. .., m). 

DMPC films. Direct measurement of interaction forces in films stabilised by neutral phospholipids has been first done with microscopic foam films from suspensions of small unilamellar DMPC vesicles [286]. Foam films formation from phospholipids is a difficult task since they are insoluble in water. Sonicated dispersions of insoluble phospholipids is an option, employed by Yamanaka et al. [287],... 

Fig. 3.47 depicts the disjoining pressure vs. thickness isotherm of microscopic foam films obtained from DMPC vesicle suspension. The vesicles were examined by electron microscopy after negative staining with 1% uranyl acetate solution as previously described [288]. More than 95% of the vesicles were of diameters between 15 and 35 nm. 

Fig. 3.47. Disjoining pressure thickness isotherm of microscopic foam films from DMPC vesicles...

Experimentally, we observed that the stability of DMPC vesicles increases by adding a small amount (>1 mol% is enough) of negatively charged phospholipids such as DMPG. 

Needham, D. and Evans, E. (1988) Struemre and mechanical properties of giant lipid (DMPC) vesicle bilayers from 20-degrees-C below to 10-degrees-C above the liquid-crystal crystalline phase transition at 24-degrees-C. Biochemistty, 27 (21), 8261-8269. 

Several years ago, Chakrabarti et al. " described for the first time such a polymerization of RNA inside DMPC vesicles by polynucleotide phosphorylase. In these experiments, ADP was added externally to the enzyme-containing vesicles (this enzymatic reaction does not require template nucleic acids for initiation) and incubated at 23°C, the main phase transition temperature of DMPC. Because of these gel-to-liquid crystalline transitions of the bilayer, the vesicles could take up ADP from the external milieu, and the enzyme could produce poly (A). On the other hand, the enzyme could not leak out because of its size. Similar experiments were also carried out in our group by Walde et al. Here, the vesicles consisted of a single-chain amphiphile (oleic acid/oleate) that forms vesicles at a pH of about 8.0. ADP was shown to permeate across the oleic acid/oleate membrane and was incorporated inside the vesicles by polynucleotide phosphorylase to poly(A). 

In a vesicle an aqueous volume (water pool) is entirely enclosed by a membrane that is basically a bilayer of lipid molecules [127-137]. In the case of the unilamellar dimyristoylphosphatidylcholine (DMPC) vesicles (radius = 250 nm) there is only one such bilayer, whereas a multilamellar vesicle (radius 1000 nm) consists of several concentric bilayers. Unilamellar vesicles can be produced from multilamellar vesicles by sonication. In such a system there are two kinds of... 

This experimental approach has been used previously to study the spontaneous transfer of phospholipids between artificial membranes (Martin and MacDonald, 1976 Duckwitz-Peterlein et al., 1977). Xti et al. (1982) used the fluorescence anisotropy of diphenylhexatriene (DPH) in the phosphatidylcholine bilayer to measure the change in the physical state of DPPC and DMPC vesicles upon mixing in the presence of transfer protein. The fluorescent measurements were recorded at a temperature intermediate between the phase transition of the two initially pure vesicles. By using flow cytometry, it was possible to measure the fluorescence... 

Although [Nle15]-gastrin-17 and [Thr,Nle]-CCK-9 are capable of binding calcium ions in TFE, they were unable to induce Ca2+ influxes into DMPC vesicles as shown in fig. 21. This fully agrees with the findings from microcalorimetric and CD measurements which excluded major interactions of these peptides with the DMPC bilayer. Conversely, the induced lipid interaction of their lipophilic derivatives DM-gastrin and DM-CCK provoked ion influxes with full equilibration... 

Zeaxanthin (C ) has been incorporated in DMPC and egg lecithin vesicles. This a,(D-bipolar carotenoid reinforces the DMPC vesicle with respect to mechanical stability and water permeability but has no effect on fluid egg lecithin membranes (Lazrak et al.,1987). Electron-poor derivatives with electron-withdrawing carboxyl or pyridinium end groups should reversibly take up electrons in a type of reversible Michael reaction and then act as organic wires. There are, however, no reports on stable anion radicals of such chro-mophores in the literature. Claims of electron transport through vesicle membranes are very probably erroneous. It has been shown by reduction of an entrapped indigo dye that bixin derivatives in DPPC vesicle membranes favor the transport of borohydride and dithionite ions through the membrane rather... 

Table 4 Overall Quenching Rate Constants for Anthracyclines Incorporated into DMPC vesicles...

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