PC Headgroups Research Articles

Influence of stigmastanol and stigmastanyl-phosphorylcholine, two plasma cholesterol lowering substances, on synthetic phospholipid membranes. A 2H- and 31P-NMR study

Cholesterol, stigmastanol, and stigmastanyl-phosphorylcholine (ST-PC) were incorporated into model membranes composed of 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine (POPC) or 1,2-dioleoyl- sn-glycero-3-phosphocholine (DOPC), POPC and ST-PC were deuterated at the lipid headgroup, DOPC at the cis-double bonds. The influence of the three sterols on the motion and conformation of the lipid headgroups and the hydrocation chains was monitored with 2H- and 31P-NMR. All three sterols were freely miscible with the lipid matrix in concentrations of up to 50 mol% without inducing phase separations or nonbilayer structures. However, the molecules exert quite different effects on the phospholipid bilayer. Cholesterol and stigmastanol are largely buried in the hydrocarbon part of the membrane, distinctly restricting the flexing motions of the fatty acyl chains whereas the conformation of the phospholipid headgroups is little affected. In contrast, ST-PC is anchored with its headgroup in the layer of phospholipid dipoles, preventing an extensive penetration of the sterol ring into the hydrocarbon layer. Hence ST-PC has almost no effect on the hydrocarbon chains but induces a characteristic conformational change of the phospholipid headgroups. The 2H- and 31P-NMR spectra of mixed phospholipid/ST-PC membranes further demonstrate that the PC headgroup of ST-PC has a similar orientation as the surrounding phosphatidylcholine headgroups. For both types of molecules the −P-N + dipole is essentially parallel to the membrane surface. Addition of ST-PC induces a small rotation of the POPC headgroup towards the water phase.

Structure of polymerizable lipid bilayers: water profile of a diacetylenic lipid bilayer using elastic neutron scattering

Elastic neutron scattering experiments have been used to study the hydration of multibilayers of 1,2- bis(10,12-tricosadiynol- sn-glycero-3- phosphocholine (DC 8,9PC). Previously published FTIR spectroscopic data had suggested, based on shifts in the carbonyl (CO) stretch frequencies, that the phosphocholine headgroup in these polymerizable lipid bilayers was much less hydrated than that of saturated phosphatidylcholines. Our results demonstrate that the DC 8,9PC headgroup is at least as well hydrated as that of dpalmitoylphosphatidylcholine (DPPC), a saturated lipid, under the same conditions.

4968. Microstructure of beam-annealed silicon: J M Gibson, J Vac Sci Technol, 18 (3), 1981, 810–817

Our previous fluorescence study has provided indirect evidence that lipid headgroup components tend to adopt regular, superlattice-like lateral distribution in fluid phosphatidylethanolamine/phosphatidylcholine (PE/PC) bilayers (Cheng et al., 1997, Biophys. J. 73:1967–1976). Here we have further studied this intriguing phenomenon by making use of the fluorescence properties of a sterol probe, dehydroergosterol (DHE). Fluorescence emission spectra, fluorescence anisotropy (r), and time-resolved fluorescence intensity decays of DHE in 1-palmitoyl-2-oleoyl-PC (POPC)/1-palmitoyl-2-oleoyl-PE (POPE) mixtures were measured as a function of POPE mole fraction (XPE) at 23°C. Deviations, including dips or kinks, in the ratio of fluorescence peak intensity at 375 nm/fluorescence peak intensity at 390 nm (I375/I390), fluorescence decay lifetime (τ), or rotational correlation time (ρ) of DHE versus PE composition plots were found at XPE ≈ 0.10, 0.25, 0.33, 0.65, 0.75, and 0.88. The critical values at XPE ≈ 0.33 and 0.65 were consistently observed for all measured parameters. In addition, the locations, but not the depth, of the dips for XPE < 0.50 did not vary significantly over 10 days of annealing at 23°C. The observed critical values of XPE coincide (within ±0.03) with some of the critical mole fractions predicted by a headgroup superlattice model proposing that the PE and PC headgroups tend to be regularly distributed in the plane of the bilayer. These results agree favorably with those obtained in our previous fluorescence study using dipyrenylPC and Laurdan probes and thus support the proposition that 1) regular arrangement within a domain exists in fluid PE/PC bilayers, and 2) superlattice formation may play a significant role in controlling the lipid composition of cellular membranes (Virtanen et al., 1998, Proc. Natl. Acad. Sci. USA. 95:4964–4969). The present data provide new information on the physical properties of such superlattice domains, i.e., the dielectric environment and rotational motion of membrane sterols appear to change abruptly as the lipid headgroups exhibit regular superlattice-like distributions in fluid bilayers.

4965. Laser annealing and epitaxy: H J Leamy, J Vac Sci Technol, 18 (2), 1981, 208–214

Our previous fluorescence study has provided indirect evidence that lipid headgroup components tend to adopt regular, superlattice-like lateral distribution in fluid phosphatidylethanolamine/phosphatidylcholine (PE/PC) bilayers (Cheng et al., 1997, Biophys. J. 73:1967–1976). Here we have further studied this intriguing phenomenon by making use of the fluorescence properties of a sterol probe, dehydroergosterol (DHE). Fluorescence emission spectra, fluorescence anisotropy (r), and time-resolved fluorescence intensity decays of DHE in 1-palmitoyl-2-oleoyl-PC (POPC)/1-palmitoyl-2-oleoyl-PE (POPE) mixtures were measured as a function of POPE mole fraction (XPE) at 23°C. Deviations, including dips or kinks, in the ratio of fluorescence peak intensity at 375 nm/fluorescence peak intensity at 390 nm (I375/I390), fluorescence decay lifetime (τ), or rotational correlation time (ρ) of DHE versus PE composition plots were found at XPE ≈ 0.10, 0.25, 0.33, 0.65, 0.75, and 0.88. The critical values at XPE ≈ 0.33 and 0.65 were consistently observed for all measured parameters. In addition, the locations, but not the depth, of the dips for XPE < 0.50 did not vary significantly over 10 days of annealing at 23°C. The observed critical values of XPE coincide (within ±0.03) with some of the critical mole fractions predicted by a headgroup superlattice model proposing that the PE and PC headgroups tend to be regularly distributed in the plane of the bilayer. These results agree favorably with those obtained in our previous fluorescence study using dipyrenylPC and Laurdan probes and thus support the proposition that 1) regular arrangement within a domain exists in fluid PE/PC bilayers, and 2) superlattice formation may play a significant role in controlling the lipid composition of cellular membranes (Virtanen et al., 1998, Proc. Natl. Acad. Sci. USA. 95:4964–4969). The present data provide new information on the physical properties of such superlattice domains, i.e., the dielectric environment and rotational motion of membrane sterols appear to change abruptly as the lipid headgroups exhibit regular superlattice-like distributions in fluid bilayers.

4972. Defect formation in heavily doped Si upon irradiation: V I Gubskaya et al, Rad Effects, 55 (1/2), 1981, 35–38

Our previous fluorescence study has provided indirect evidence that lipid headgroup components tend to adopt regular, superlattice-like lateral distribution in fluid phosphatidylethanolamine/phosphatidylcholine (PE/PC) bilayers (Cheng et al., 1997, Biophys. J. 73:1967–1976). Here we have further studied this intriguing phenomenon by making use of the fluorescence properties of a sterol probe, dehydroergosterol (DHE). Fluorescence emission spectra, fluorescence anisotropy (r), and time-resolved fluorescence intensity decays of DHE in 1-palmitoyl-2-oleoyl-PC (POPC)/1-palmitoyl-2-oleoyl-PE (POPE) mixtures were measured as a function of POPE mole fraction (XPE) at 23°C. Deviations, including dips or kinks, in the ratio of fluorescence peak intensity at 375 nm/fluorescence peak intensity at 390 nm (I375/I390), fluorescence decay lifetime (τ), or rotational correlation time (ρ) of DHE versus PE composition plots were found at XPE ≈ 0.10, 0.25, 0.33, 0.65, 0.75, and 0.88. The critical values at XPE ≈ 0.33 and 0.65 were consistently observed for all measured parameters. In addition, the locations, but not the depth, of the dips for XPE < 0.50 did not vary significantly over 10 days of annealing at 23°C. The observed critical values of XPE coincide (within ±0.03) with some of the critical mole fractions predicted by a headgroup superlattice model proposing that the PE and PC headgroups tend to be regularly distributed in the plane of the bilayer. These results agree favorably with those obtained in our previous fluorescence study using dipyrenylPC and Laurdan probes and thus support the proposition that 1) regular arrangement within a domain exists in fluid PE/PC bilayers, and 2) superlattice formation may play a significant role in controlling the lipid composition of cellular membranes (Virtanen et al., 1998, Proc. Natl. Acad. Sci. USA. 95:4964–4969). The present data provide new information on the physical properties of such superlattice domains, i.e., the dielectric environment and rotational motion of membrane sterols appear to change abruptly as the lipid headgroups exhibit regular superlattice-like distributions in fluid bilayers.