Mechanism of the Leakage Induced on Lipid Model Membranes by Rz1 Lipoprotein, the Bacteriophage λ Rz1 Gene Product: A Fluorescence Study

The leakage of aqueous contents of neutral (dipalmitoylphosphatidylcholine/cholesterol) liposomes as induced by Rz1, a proline-rich lipoprotein, the bacteriophage Rz1 gene product, was studied. Fluorescence enhancement assay with Tb³⁺/dipicolinic acid and self-quenching assays with carboxyfluorescein and fluorescein isothiocyanaten-dextran were used to monitor the Rz1-induced leakage from neutral liposomes. The results demonstrated that Rz1 caused local membrane destabilization leading to the leakage of the liposome contents. The extent of the leakage was independent of the molecular mass of the liposome-entrapped solutes in the range of 376–4000 Da. The kinetics of Rz1-liposome leakage was very similar to that obtained with detergent Triton X-100 for all the solutes used. The results suggested that Rz1 can act as a detergent; i.e., by interacting with lipids on both sides of the liposome membranes (inducing perturbation in the lipid packing within the bilayer), it facilitates the transfer of encapsulated molecules into the external liposome environment. The importance of this result for Rz1 physiological function is discussed.     

Preparation of lucifer yellow fluorescent liposomes: A method for cells' membrane labeling

This report describes a method to conjugate lucifer yellow to the external surface of liposomes. The heterobifunctional cross-linking reagentN-succinimidyl 3-(2-pyridyldithio)propionate has been used to activate DMPE molecules. The DMPE-dithiopyridine product has been mixed with DMPC to prepare liposome vesicles. These have been reduced by DTT and finally reacted with lucifer yellow-iodoacetamide to produce the fluorescence-labeled vesicles. The quenching of their fluorescence intensity by Kl is consistent with fully exposed fluorophores. The decay of the fluorescence intensity of the lipid-bound lucifer yellow is biexponential (₁=7.9 ns; ₂=1.1 ns), with a relative yield of 0.16. When the fluorescent liposomes are mixed with cells, the lucifer yellow-DMPE derivative is transferred. Boar spermatozoa and peripheral human blood lymphocytes have been used as cellular models. The extent of incorporation is dependent on the incubation time and temperature. At 36°C, lucifer yellow fluorescence appears in the spermatozoa cells after 10 min of incubation and reaches its maximum at about 60 min. The fluorescent phospholipid derivative seems to incorporate specifically into membrane structures. The highest labeling ratio is observed with integer, scarcely motile, spermatozoa. A poorer labeling yield (15%) is found with lymphocytes. Interestingly, photobleaching due to epiillumination of the labeled cells is apparently negligible and cells are clearly visible after irradiation times ranging from several minutes to few hours.A preliminary account of this work was presented at the Quarto Simposio su Biotecnologie Biochimiche, Capri, 28–30 June 1992.     

Interaction of dipalmitoyl phosphatidylcholine (DPPC) liposomes and insulin

Insulin, a peptide that has been used for decades in the treatment of diabetes, has well-defined properties and delivery requirements. Liposomes, which are lipid bilayer vesicles, have gained increasing attention as drug carriers which reduce the toxicity and increase the pharmacological activity of various drugs. The molecular interaction between (uncharged lipid) dipalmitoyl phosphatidylcholine (DPPC) liposomes and insulin has been characterized by using Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction. The characteristic protein absorption band peaks, Amide I (at about 1660?cm^?1) and Amide II band (at about 1546?cm^?1) are potentially reduced in the liposome insulin complex. Wide-angle x-ray scattering measurements showed that the association of insulin with DPPC lipid of liposomes still maintains the characteristic DPPC diffraction peaks with almost no change in relative intensities or change in peak positions. The absence of any shift in protein peak positions after insulin being associated with DPPC liposomes indicates that insulin is successfully forming complex with DPPC liposomes with possibly no pronounced alterations in the structure of insulin molecule.     

Effect of neutral particles on high-frequency conductivity of plasma

Diagram technique of the temperature-dependent Green's functions is used to study the effect of neutral particles on the high-frequency conductivity of high-temperature plasma in the Born approximation. Assuming that the frequency of the electric field is much larger than the collision frequency of the electrons with neutral particles, expressions are derived for Re ^en () in two cases: 1. the neutral particles and electrons are regarded as hard, elastic spheres, 2. the neutral particles are hydrogen atoms in the ground state.In conclusion the author thanks J. Teichmann, C.Sc., for suggesting this work and for valuable discussions.     

Measurement and QCD analysis of neutral and charged current cross sections at HERA

The inclusive e⁺p single and double differential cross sections for neutral and charged current processes are measured with the H1 detector at HERA. The data were taken in 1999 and 2000 at a centre-of-mass energy of and correspond to an integrated luminosity of 65.2 pb^-1. The cross sections are measured in the range of four-momentum transfer squared Q² between 100 and and Bjorken x between 0.0013 and 0.65. The neutral current analysis for the new e⁺p data and the earlier e^-p data taken in 1998 and 1999 is extended to small energies of the scattered electron and therefore to higher values of inelasticity y, allowing a determination of the longitudinal structure function F_L at high Q² ( ). A new measurement of the structure function is obtained using the new e⁺p and previously published neutral current cross section data at high Q². These data together with H1 low Q² precision data are further used to perform new next-to-leading order QCD analyses in the framework of the Standard Model to extract flavour separated parton distributions in the proton.Arrival of the final proofs: 11 July 2003     

Continuous wave laser operation of Yb<Superscript>3+</Superscript>:YVO<Subscript>4</Subscript>

We have demonstrated the continuous wave laser operation of Yb³⁺:YVO₄. For Ti:Al₂O₃ laser pumping at 985 nm, a maximum slope efficiency of 41.1% and a threshold pump power of 76 mW were obtained. The maximum output power was 433 mW at a laser wavelength of 1037 nm.Using a cw diode laser around 974 nm as a pump source, a slope efficiency of 10.9% and a maximum output power of 152 mW were achieved at a laser wavelength of 1039 nm. The laser threshold pump power was 608 mW with respect to the absorbed pump power. The effective emission cross-sections for the ²F_5/2²F_7/2 transition were determined using the Füchtbauer–Ladenburg equation. The maxima of the effective absorption and emission cross-sections were found at 984.5 nm (6.74×10^-20 cm²) in -po larization and 985.5 nm (4.28×10^-20 cm²) also in -p olarization. The upper laser level lifetime was measured with suppression of radiation trapping and is around 318 s. PACS 42.55.Rz; 42.55.Xi; 42.70.Hj     

Determination of the partition coefficients of the nonionic detergent C12E7 between lipid-detergent mixed membranes and water by means of Laurdan fluorescence spectroscopy

The membrane-water partition coefficient of the detergent C₁₂E₇ between water and C₁₂E₇/POPC mixed membranes has been determined by means of steady-state fluorescence spectroscopy. The emission spectra of the fluorescent probe Laurdan were used as an indicator of membrane composition at different membrane concentrations in the sample. The partition coefficient expressed as the ratio of the mole fractions of the detergent in the membrane and water phases is about 6^*10⁵ at low molar ratios of C₁₂E₇/POPC (R _c ) and decreases rapidly with increasingR _c . The limiting detergent content of the lamellar phase (R _c ^* >0.8) is indicated by a minimum ofP(R _c ).     

Laser evaporation as a source of small free radicals

It is shown that laser evaporation of a solid target followed by adiabatic expansion can be used to produce cold beams of neutral small open shell molecules. LIF is applied to detect CuH (X ¹), CH (X ²), SiH (X ²), CuO (X ²), and FeO (X ⁵). A production of 10^9±1 molecules/sr in a single pulse is obtained for SiH. For a copper target, the optical emission of the jet plume is discussed.     

Paramagnetic Liposomes as Thermosensitive Probes for MRI-Guided Thermal Treatment: In Vitro Feasibility Studies

In this work the potential of thermosensitive paramagnetic liposomes for in vitro temperature monitoring during radiofrequency heating has been assessed. Two thermosensitive liposome formulations with different phase-transition properties were investigated. Temperature-dependent spin–lattice (T ₁) relaxivity measurements were performed at 0.24 T. Magnetic resonance imaging was performed at 2 T in liposome-containing phantom models and T ₁ relaxation rates (R ₁) were quantified as a function of temperature. Independent temperature measurements were performed using both thermocouple and magnetic-resonance-based methods (proton resonance frequency and diffusion-based thermometry). The relaxometric measurements showed that the T ₁ relaxivity increased from low values (about 0.3 s⁻¹mM⁻¹ at 35 °C) to about 4 s⁻¹mM⁻¹ when the temperature approached and exceeded the phase-transition temperature (T _c) of the liposome preparations. These data correlated well to the imaging data where an increased signal intensity was observed on T ₁-weighted images at temperatures above T _c. The derived R ₁ maps reflected the measured liposomal temperature sensitivity and temperature quantification was possible on the basis of the measured linear temperature versus R ₁ correlation in the transition range of the liposomes. The studies have therefore shown that thermosensitive paramagnetic liposomes exhibit the required temperature sensitivity to allow for an accurate mapping of the temperature changes in an in vitro imaging model. Authors' address: Kamil A. Il'yasov, Physics Department, Kazan State University, Kremlevskaya ulitsa 18, Kazan 420008, Russian Federation     

Distribution of merocyanine 540 in phospholipid membranes

The interaction of the fluorescent photosensitizer merocyanine 540 (MC-540) with model phospholipid membranes was studied. Two different-colored species (monomers and dimers) of MC-540 were registered in phospholipid liposomes. Variations in both phospholipid composition (DMPC, DPPC, POPC, egg PC) and temperature (15–60°C) resulted in changes in the MC-540 monomerdimer distribution. The values of the monomer-dimer equilibrium constant of MC-540 in egg PC (K=14.8 M), in POPC (K=26.7 M), and in DMPC (K=271.0 M) were determined at the temperature of 23±2°C. Suppression of MC-540 association with phospholipid bilayers was provoked by the addition of albumin to a liposome suspension. Albumin was observed to compete very successfully with lecithins containing saturated fatty acid chains (DPPC, DMPC), while only a weak competition of albumin with unsaturated lecithins (POPC, egg PC) for binding MC-540 molecules was registered.