Influence of vitamin E acetate and other lipids on the phase behavior of mesophases based on unsaturated monoglycerides

The phase behavior of the ternary unsaturated monoglycerides (UMG)-DL-α-tocopheryl acetate-water system has been studied. The effects of lipid composition in both bulk and dispersed lyotropic liquid crystalline phases and microemulsions were investigated. In excess water, progressive addition of DL-α-tocopheryl acetate to a binary UMG mixture results in the following phase sequence: reversed bicontinuous cubic phase, reversed hexagonal (H(II)) phase, and a reversed microemulsion. The action of DL-α-tocopheryl acetate is then compared to that of other lipids such as triolein, limonene, tetradecane, and DL-α-tocopherol. The impact of solubilizing these hydrophobic molecules on the UMG-water phase behavior shows some common features. However, the solubilization of certain molecules, like DL-α-tocopherol, leads to the presence of the reversed micellar cubic phase (space group number 227 and symmetry Fd3m) while the solubilization of others does not. These differences in phase behavior are discussed in terms of physical-chemical characteristics of the added lipid molecule and its interaction with UMG and water. From an applications point of view, phase behavior as a function of the solubilized content of guest molecules (lipid additive in our case) is crucial since macroscopic properties such as molecular release depend strongly on the phase present. The effect of two hydrophilic emulsifiers, used to stabilize the aqueous dispersions of UMG, was studied and compared. Those were Pluronic F127, which is the most commonly used stabilizer for these kinds of inverted type structures, and the partially hydrolyzed emulsifier lecithin (Emultop EP), which is a well accepted food-grade emulsifier. The phase behavior of particles stabilized by the partially hydrolyzed lecithin is similar to that of bulk sample at full hydration, but this emulsifier interacts significantly with the internal structure and affects it much more than F127.

SAXS Study on Azithromycin Loaded Nonionic Microemulsions

Structure of water/propylene glycol/ethoxylated mono-di-glyceride/peppermint oil/ethanol microemulsions solubilizing azithromycin has been investigated at room temperature by small-angle X-ray scattering (SAXS) technique. The scattering data were evaluated by Indirect Fourier Transformation (IFT) or Generalized Indirect Fourier Transformation (GIFT) methods depending on the aqueous phase content. The growth of the microemulsions droplets by increasing the water content and the effect of azithromycin incorporation in the microemulsions were investigated. The Indirect Fourier Transformation gives the real space pair-distance distribution function: a facile way for the quantitative estimation of structure parameters of the microemulsions. It was found that the size of the microemulsion aggregates or repeating distances in the microemulsion increases with the aqueous phase content. The maximum diameter of the drug free and drug loaded microemulsions aggregates depend on their microstructure. The values of the effective interaction radius of the microemulsions are higher for the drug free compared to the drug loaded microemulsions aggregates.

Adsorption of anionic and cationic surfactants on anionic colloids: supercharging and destabilization

We present herein a study on the adsorption of anionic (SDS), cationic (CTAB), and nonionic (C(12)E(5)) surfactants onto anionic silica nanoparticles. The effects of this adsorption are studied by means of the static structure factor, S(q), and the collective diffusion coefficient, D(c), obtained from small-angle X-ray scattering and dynamic light scattering measurements, respectively. The effective charge on the particles was determined also from classical electrophoresis and electroacoustic sonic-amplitude measurements. The surface tension of the sample was also investigated. Of particular note is the adsorption of SDS onto the silica nanoparticles, which leads to supercharging of the interface. This has interesting repercussions for structures obtained by the layer-by-layer (LbL) technique, because emulsions stabilized with supercharged and hydrophobized silica are perfect candidates for use in a multilayer system.

The effect of enzyme concentration on the rate of the hydrolysis of cellulose

The relationship among extent of hydrolysis, reaction time, and enzyme dosage was investigated. For this, Sigmacell 50 and pretreated poplar wood (20 g/L) was hydrolyzed with varying dosages of cellulases from three different sources (5 to 100 FPU/g) for time periods ranging from 2 to 94 h. It was found that the formation of glucose can be described by summation of two parallel first order reactions. The extent of hydrolysis at fixed time increases with increasing enzyme dosage in a hyperbolic function. From the empirical data it is possible to calculate the fractions of easily and difficult hydrolyzable cellulose and the digestability which could maximally be obtained at infinite enzyme loadings. In the system Sigmacell 50 and Celluclast the easily and difficult hydrolyzable components are 43.0 and 57.0%, respectively, and the maximum digestability at 94 h is 82.6%. Poplar wood, steam treated at 200 degrees , 220 degrees , and 240 degrees C, showed with Celluclast at 24 h a maximum digestability (weight percentage of wood degraded to glucose) of 43.9, 64.9, and 68.0%. The relationships derived from experimental data allow one to compare objectively the effectiveness of different cellulase enzymes and different pretreatments.

Dynamic light scattering in turbid colloidal dispersions: A comparison between the modified flat-cell light-scattering instrument and 3D dynamic light-scattering instrument

It remains a challenge to measure dynamics in dense colloidal systems. Multiple scattering and low light-transmission rates often hinder measurements in such systems. One of the well-established techniques for overcoming the problem of multiple scattering is cross-correlation techniques such as 3D dynamic light scattering (3D-DLS). However, a high degree of multiple scattering, i.e., vanishing single-scattering contribution in the signal, limits the use of the 3D-DLS technique. We present another approach to measure turbid media by way of upgrading our flat-cell light-scattering instrument (FCLSI). This instrument was originally designed for static light-scattering (SLS) experiments and is similar to a Fraunhofer setup, which features a flat sample cell. The thickness of the flat sample cell can be varied from 13 mum to 5 mm. The small thickness increases the transmission, reduces multiple scattering to a negligible amount, and therefore enables the investigation of dense colloidal systems. We upgraded this instrument for DLS measurements by the installation of an optical single-mode fiber detector in the forward scattering regime. We present our instrumentation and subsequently test its limits using a concentration series of a turbid colloidal suspension. We compare the performances of our modified flat-cell light-scattering instrument with that of standard DLS and with that of 3D-DLS. We show that 3D-DLS and FCLSI only have a comparable performance if the length of the light path in the sample using the 3D-DLS is reduced to a minimum. Otherwise, the FCLSI has some advantage.

Small-Angle Scattering from Hexagonal Liquid Crystals

In this paper, we discuss the scattering behavior of two-dimensional hexagonal liquid crystals with micellar cylinders as a building unit. We treat the hexagonal phase as an accumulation of ordered domains of finite size that typically consists of one hundred parallel cylinders whose axes are perpendicular to the lattice plane. When we suppose that no specific orientation is preferred, the lengths of the cylinders are rather large compared to their diameter, and the polydispersity of the size of the cylinders is negligible; it is therefore possible to split the scattering intensity into a product of the so-called form factor and the structure factor. This product approximation is the basic condition for the use of the generalized indirect Fourier transformation (GIFT) method and the deconvolution (DECON) method to evaluate the small-angle scattering data of hexagonal phases. The GIFT method provides the parameters of the structure factor model and the pair distance distribution function of the cylinders. Via the DECON technique, we can calculate the radial contrast profile of the cylinders from the pair distance distribution function that is obtained by the GIFT method.

Crystallography of dispersed liquid crystalline phases studied by cryo-transmission electron microscopy

Low molecular weight surfactants, for example monoglycerides and phospholipids, form a multitude of self-assembled structures, such as inverted cubic or hexagonal mesophases, if brought into contact with water/oil. These mesophases can be dispersed in water using adequate surface-active materials such as low molecular weight surfactants or surface active polymers. In order to use such mesophase particles for incorporating drugs and aromas, it is essential to determine their internal crystallographic structure and to understand their mechanism of stabilization. Cryo-transmission electron microscopy was used to investigate the internal structure of different dispersed particles at various temperatures and oil contents. It is shown here that cryo-transmission electron microscopy, in combination with fast Fourier transform and tilting experiments, is effective in obtaining information on crystallographic structure, space group and morphology of particles with reversed bicontinuous cubic and hexagonal structures. In particular, using the presence or the absence of the {111} reflections and viewing the same particle under different axes of observation allows one to discriminate between the Im3m and Pn3m space groups. A major advantage of cryo-transmission electron microscopy is the ability to analyse single particles. This allows the identification of particles present at very low concentrations and the coexistence of particles with different internal self-assembly structures. With this technique we have obtained strong evidence for the presence of two cubic internal self-assembly structures with different space groups within the same dispersion. In addition, we found that cryo-transmission electron microscopy combined with tilting experiments enables the analysis of internal particle morphology, allowing the discussion of mechanisms for hexosome stabilization.

Growth and structure of α-lactalbumin nanotubes

Partial hydrolysis of α-lactalbumin by a protease fromBacillus licheniformisunder appropriate conditions leads to the formation of nanotubular structures. The growth of α-lactalbumin nanotubes and their dimensions were analysed using transmission electron microscopy, static light scattering and small-angle X-ray scattering. The scattering data were fitted using a model describing the growth of the tubes and using the form factor of a hollow tube. The cylinder diameter was calculated to be 19.9 (2) nm and the cavity diameter 8.7 (7) nm. The elongation rate of the nanotubes was about 10 nm min−1under the experimental conditions.

A preliminary study of breast cancer diagnosis using laboratory based small angle x-ray scattering

Breast tissue collected from tumour samples and normal tissue from bi-lateral mastectomy procedures were examined using small angle x-ray scattering. Previous work has indicated that breast tissue disease diagnosis could be performed using small angle x-ray scattering (SAXS) from a synchrotron radiation source. The technique would be more useful to health services if it could be made to work using a conventional x-ray source. Consistent and reliable differences in x-ray scatter distributions were observed between samples from normal and tumour tissue samples using the laboratory based 'SAXSess' system. Albeit from a small number of samples, a sensitivity of 100% was obtained. This result encourages us to pursue the implementation of SAXS as a laboratory based diagnosis technique.

Lipoprotein lipase mediates the uptake of glycated LDL in fibroblasts, endothelial cells, and macrophages

The nonenzymatic glycation of LDL is a naturally occurring chemical modification of apolipoprotein (apo)-B lysine residues by glucose. Once glycated, LDL is only poorly recognized by lipoprotein receptors including the LDL receptor (LDL-R), the LDL-R-related protein (LRP), and scavenger receptors. Glycated LDL (gLDL) is a preferred target for oxidative modifications. Additionally, its presence initiates different processes that can be considered "proatherogenic." Thus, LDL glycation might contribute to the increased atherosclerotic risk of patients with diabetes and familial hypercholesterolemia. Here we investigate whether lipoprotein lipase (LPL) can mediate the cellular uptake of gLDL. The addition of exogenous LPL to the culture medium of human skin fibroblasts, porcine aortic endothelial cells, and mouse peritoneal macrophages enhanced the binding, uptake, and degradation of gLDL markedly, and the relative effect of LPL on lipoprotein uptake increased with the degree of apoB glycation. The efficient uptake of gLDL by LDL-R-deficient fibroblasts and LRP-deficient Chinese hamster ovary cells in the presence of LPL suggested a mechanism that was independent of the LDL-R and LRP. In macrophages, the uptake of gLDL was also correlated with their ability to produce LPL endogenously. Mouse peritoneal macrophages from genetically modified mice, which lacked LPL, exhibited a 75% reduction of gLDL uptake compared with normal macrophages. The LPL-mediated effect required the association of the enzyme with cell surface glycosaminoglycans but was independent of its enzymatic activity. The uptake of gLDL in different cell types by an LPL-mediated process might have important implications for the cellular response after gLDL exposure as well as the removal of gLDL from the circulation.

Room temperature activates human blood platelets

Temperatures ranging from room temperature (20 degrees C) to 42 degrees C are generally not considered to have an activating effect on platelets. However, this assumption is not supported by clinical phenomena that result in hemostatic failure related to hypothermia. In this study, we investigated the effect of temperatures between room temperature (20 degrees C) and 42 degrees C on human blood platelets and found that room temperature causes marked activation of platelets. Major changes in platelet morphology were seen at 20 degrees C compared to resting platelets at 37 degrees C. Platelet morphology was investigated with noninvasive live cell techniques (light microscopy and dynamic and static light scattering), as well as with transmission and scanning electron microscopy. The changes in platelet morphology correlated with the expression of the activation marker, activated glycoprotein (GP) IIb-IIIa, measured by flow cytometry. Twenty-five percent to 30% of platelets expressed activated GPIIb-IIIa after exposure to 20 degrees C for 10 minutes. In the presence of serotonin re-uptake inhibitors, the serotonin content of platelets at 20 degrees C was twice that of resting platelets. In comparison, moderate heat shock conditions (42 degrees C for 10 minutes) caused no signs of platelet activation as indicated by the absence of morphological alterations, no expression of activated GPIIb-IIIa, and no changes in serotonin content. These results show that room temperature by itself significantly activates platelets and has an effect on the platelet serotonin content. This may contribute to both the functional lesion associated with 22 degrees C storage of platelets for transfusion and the in vivo hemostatic failure after hypothermia.

Electrospray ionization mass spectrometry, circular dichroism and SAXS studies of the (S)-hydroxynitrile lyase from Hevea brasiliensis

We report on experiments pertaining to solution properties of the (S)-hydroxynitrile lyase from Hevea brasiliensis (HbHNL). Small angle X-ray scattering unequivocally established the enzyme to occur in solution as a dimer, presumably of the same structure as in the crystal. The acid induced, irreversible deactivation of HbHNL was examined by electrospray ionization mass spectrometry (ESI-MS), circular dichroism (CD) and by measuring the enzyme activity. The deactivation is paralleled by an unfolding of the enzyme. ESI-MS of this 30000 Da per monomer heavy protein demonstrated that unfolding took place in several stages which are paralleled by a decrease in enzyme activity. Unfolding can also be observed by CD spectroscopy, and there is a clear correlation between enzyme activity and unfolding as detected by ESI-MS and CD.

Synthetic phospholipid analogs: a structural investigation with scattering methods

The phase behavior of the newly synthesized phospholipid analogs is necessary to be known because of the importance of the structure of the phospholipid analogs for the activity against tumor cell lines. The type of aggregates formed under defined conditions, the size distribution and the internal structure of the particles as well as stability upon storage are examined by scattering methods. Octadecyl-methyl-glycero-phosphocholine (OMGPC) and Octadecyl-imidazoyl-deoxy-glycero-phosphocholine (OIDGPC) are cytostatic systems designed synthetically for the medical application and, therefore, prepared and measured usually at 37 degrees C. Both phospholipid analogs behave under the same conditions almost similarly. They show also the similar behavior in long term studies like the biological ganglioside GM1. Under physiological conditions, OMGPC and OIDGPC form spherical micelles with a maximum dimension of about 8 nm, which do not change with concentration.

Solving the generalized indirect Fourier transformation (GIFT) by Boltzmann simplex simulated annealing (BSSA)

The structure of colloidal particles can be studied with small-angle X-ray and neutron scattering (SAXS and SANS). In the case of randomly oriented systems, the indirect Fourier transformation (IFT) is a well established technique for the calculation of model-free real-space information. Interaction leads to an overlap of inter- and intraparticle scattering effects, preventing most detailed interpretations. The recently developed generalized indirect Fourier transformation (GIFT) technique allows these effects to be separated by assuming various models for the interaction,i.e.the so-called structure factors. The different analytical behaviour of these structure factors from that of the form factors, describing the intraparticle scattering, allows this separation. The mean-deviation surface is defined by the quality of the fit for different parameter sets of the structure factor. Its global minimum represents the solution. The former non-linear least-squares approach has proved to be inefficient and not very reliable. In this paper, the incorporation of the completely different Boltzmann simplex simulated annealing (BSSA) algorithm for finding the global minimum of the hypersurface is presented. This new method increases not only the calculation speed but also the reliability of the evaluation.

Comparison of HOCl traps with myeloperoxidase inhibitors in prevention of low density lipoprotein oxidation

In this study, the production of the highly toxic oxidant hypochlorous acid (HOCl) by the phagocytic enzyme myeloperoxidase (MPO) was quantitated and the concomitant alterations of low density lipoprotein (LDL) were analyzed in view of the potential role of LDL in atherosclerosis. Using the monochlorodimedone assay, it was found that HOCl is produced in micromolar concentrations. The kinetics of the decrease of tryptophan fluorescence appeared to be a sensitive method to monitor LDL alterations under near in vivo conditions. Therefore, this method was used to subsequently compare the effectiveness of MPO inhibitors that block production of HOCl with compounds that act as HOCl traps. The efficiency of MPO inhibitors to prevent LDL damage increased in the series benzohydroxamic acid < salicylhydroxamic acid < 3-amino-1,2,4-triazole < sodium azide < potassium cyanide < p-hydroxy-benzoic acid hydrazide, while for the HOCl traps the protective efficiency increased in the series glycine < taurine < methionine. We conclude that HOCl traps may have high potential therapeutic impact in vivo due to their low toxicity, although high concentrations of them would have to reach sites of inflammation. In contrast, only low concentrations of a specific MPO inhibitor would be required to irreversibly inhibit the enzyme.

Lipoprotein-associated alpha-tocopheryl-succinate inhibits cell growth and induces apoptosis in human MCF-7 and HBL-100 breast cancer cells

alpha-Tocopheryl succinate (alpha-TS) is a potent inhibitor of tumor cell proliferation. The goal of the present study was to investigate whether and to what extent alpha-TS associates with plasma lipoproteins and if alpha-TS-enriched lipoproteins inhibit breast cancer cell growth in a manner comparable to the free drug. In vitro enrichment of human plasma revealed that alpha-TS readily associated with the main lipoprotein classes, findings confirmed in vivo in mice. At the highest alpha-TS concentrations, lipoproteins carrying 50000 (VLDL), 5000 (LDL) and 700 (HDL) alpha-TS molecules per lipoprotein particle were generated. alpha-TS enrichment generated lipoprotein particles with slightly decreased density and increased particle radius. To study whether the level of LDL-receptor (LDL-R) expression affects alpha-TS uptake from apoB/E containing lipoprotein particles human breast cancer cells with low (MCF-7) and normal (HBL-100) LDL-R expression were used. The uptake of free, VLDL- and (apoE-free) HDL(3)-associated alpha-TS was nearly identical for both cell lines. In contrast, uptake of LDL-associated alpha-TS by HBL-100 cells (normal LDL-R expression) was about twice as high as compared to MCF-7 cells (low LDL-R expression). VLDL and LDL-associated alpha-TS inhibited proliferation most effectively at the highest concentration of alpha-TS used (100% inhibition of MCF-7 growth with 20 microg/ml of lipoprotein-associated alpha-TS). However, also alpha-TS-free VLDL and LDL inhibited HBL-100 cell proliferation up to 55%. In both cell lines, alpha-TS-enriched HDL(3) inhibited cell growth by 40-60%. Incubation of both cell lines in the presence of free or lipoprotein-associated alpha-TS resulted in DNA fragmentation indicative of apoptosis. Collectively, the present findings demonstrate that: (1) alpha-TS readily associates with lipoproteins in vitro and in vivo; (2) the lipoprotein-enrichment efficacy was dependent on the particle size and/or the triglyceride content of the lipoprotein; (3) uptake of LDL-associated alpha-TS was apparently dependent on the level of LDL-R expression; and (4) lipoproteins were efficient alpha-TS carriers inducing reduced cell proliferation rates and apoptosis in human breast cancer cells as observed for the free drug.

Lateral microheterogeneity of diphenylhexatriene-labeled choline phospholipids in the erythrocyte ghost membrane as determined by time-resolved fluorescence spectroscopy

Choline phospholipids are the major constituents of the outer layer of the erythrocyte membrane. To investigate their lateral membrane organization we determined the fluorescence lifetime properties of diphenylhexatriene analogues of phosphatidylcholine, choline plasmalogen, (the respective enolether derivative), and sphingomyelin inserted into the outer layer of hemoglobin-free ghosts. Fluorescence lifetimes were recorded by time-resolved phase and modulation fluorometry and analyzed in terms of Continuous Lorentzian distributions. To assess the influence of membrane proteins on the fluorescence lifetime of the labeled lipids in the biomembrane, lipid vesicles were used as controls. In general, the lifetime distributions in the ghost membranes are broad compared to vesicles. Phosphatidylcholine and sphingomyelin exhibit very similar lifetime distributions in contrast to an increased plasmalogen lifetime heterogeneity in both systems. Orientational effects of side chain mobilities on the observed lifetimes can be excluded. Fluorescence anisotropies revealed identical values for all three labeled phospholipids in the biomembrane.

Thermodynamic properties and DNA binding of the ParD protein from the broad host-range plasmid RK2/RP4 killing system

ParD is a small, acidic protein from the partitioning system of the plasmid RK2/RP4. The ParD protein exhibits specific DNA binding activity and, as the antidote component of a toxin-antidote plasmid addiction system, ParD forms a tight complex in solution with its toxin antagonist, the ParE protein. Unopposed ParE acts as a toxin that causes growth retardation and killing of plasmid cured cells. ParD negatively autoregulates its expression by binding to an operator sequence in the parDE promoter region. This DNA binding activity is crucial for the regulation of the relative abundance of toxin and antidote which ultimately determines life or death for the bacterial host and its daughter cells. In light scattering studies and gel filtration chromatography we observed the existence of a stable dimer of ParD in solution. The stoichiometry of ParD-DNA complex formation appeared to be 4:1, the molecular mass of the complex was 72.1 kDa. The alpha-helical content of ParD as determined by CD-spectrometry was 35%. The protein exhibited high thermostability with a T(M) of 64 degrees C and deltaH of 25 kcal/mol as shown by differential scanning calorimetry. Upon complex formation the T(M) increased by 10 degrees C. The thermal unfolding of the ParD protein was highly reversible as observed in repeated DSC scans of the same sample. The recovery of the native fold was proven by CD-spectroscopy.

Molecular dynamics of microbial lipases as determined from their intrinsic tryptophan fluorescence

We have studied the intrinsic tryptophan fluorescence of the lipases from Chromobacterium viscosum (CVL), Pseudomonas species (PSL), and Rhizopus oryzae (ROL) in aqueous buffer, zwitterionic detergent micelles, and isopropanol-water mixtures. It was the purpose of this study to obtain information about biophysical properties of the respective enzymes under conditions that modulate enzyme activities and stereoselectivities to a significant extent. According to their decay-associated emission spectra, CVL tryptophans are located in the hydrophobic interior of the protein. In contrast, the PSL and ROL tryptophans are probably confined to the core and the surface of the lipase. From the tryptophan lifetime distributions it can be concluded that the conformation of CVL is not much affected by detergent or organic solvent (isopropanol). Accordingly, CVL is enzymatically active in these systems and most active in the presence of isopropanol. In contrast, ROL and PSL show high conformational mobility, depending on the solvent, because their lifetime distributions are very different in the presence and absence of detergent or isopropanol. Time-resolved anisotropy studies provided evidence that the lipases exhibit very high internal molecular flexibility. This peculiar feature of lipases is perhaps the key to the great differences in activity and stereoselectivity observed in different reaction media. Furthermore, information about self-association of the lipases in different solvents could be obtained. PSL, but not CVL and ROL, forms aggregates in water. Lipase aggregation can be reversed by the addition of detergent or isopropanol, which competes for the hydrophobic surface domains of this protein. This dissociation could efficiently contribute to the increase in lipase activity in the presence of a detergent or isopropanol.

Characterization of Enzymatically Induced Aggregation of Casein Micelles in Natural Concentration by in Situ Static Light Scattering and Ultra Low Shear Viscosimetry

The aggregation of casein micelles in undiluted skim milk after the addition of chymosin was studied by static light scattering and ultra low shear viscometry. The static light scattering measurements were made with two different sample thicknesses, 72 and 16 µm. The scattering data were analyzed by indirect Fourier transformation and by the polydispersity inversion technique which led to pair distance distribution functions and size distribution function, respectively. The minimum scattering angle was 1 degrees, which allows for the determination of particle sizes up to a maximum diameter of 12 µm. The fractal dimension determined from double logarithmic plots of intensity versus scattering vector resulted in values between 1.9 and 2.0. The influence of multiple scattering was determined by comparison of the measurements with the different sample thicknesses. The measurements show no significant influence of multiple scattering when the transmission is above 0.85. Due to the very complex and porous structure of the casein aggregates the Rayleigh-Debye-Gans scattering theory has been used in the data analysis. Measurements with a new instrument using ultra low shear showed good agreement with theory. Copyright 1999 Academic Press.

Small-angle scattering of interacting particles. II. Generalized indirect Fourier transformation under consideration of the effective structure factor for polydisperse systems

The indirect Fourier transformation (IFT) is the method of choice for the model-free evaluation of small-angle scattering data. Unfortunately, this technique is only useful for dilute solutions because, for higher concentrations, particle interactions can no longer be neglected. Thus an advanced technique was developed as a generalized version, the so-called generalized indirect Fourier transformation (GIFT). It is based on the simultaneous determination of the form factor, representing the intraparticle contributions, and the structure factor, describing the interparticle contributions. The former can be determined absolutely free from model assumptions, whereas the latter has to be calculated according to an adequate model. In this paper, various models for the structure factor are compared,e.g.the effective structure factor for polydisperse hard spheres, the averaged structure factor, the local monodisperse approximation and the decoupling approximation. Furthermore, the structure factor for polydisperse rod-like particles is presented. As the model-free evaluation of small-angle scattering data is an essential point of the GIFT technique, the use of a structure factor without any influence of the form amplitude is advisable, at least during the first evaluation procedure. Therefore, a series of simulations are performed to check the possibility of the representation of various structure factors (such as the effective structure factor for hard spheres or the structure factor for rod-like particles) by the less exact but much simpler averaged structure factor. In all the observed cases, it was possible to recover the exact form factor with a free determined parameter set for the structure factor. The resulting parameters of the averaged structure factor have to be understood as apparent model parameters and therefore have only limited physical relevance. Thus the GIFT represents a technique for the model independent evaluation of scattering data with a minimum ofa prioriinformation.

Time and temperature dependent aggregation behaviour of the ganglioside GM1 in aqueous solution

Gangliosides are marked amphiphiles with several ramified sugar rings and a ceramide moiety. Therefore they form micelles in aqueous solution. This aggregation behavior is studied with static and dynamic light scattering and small angle X-ray scattering. The shape and the size of the GM1 micelles in dependence of time and temperature are investigated. Some data have been published recently where two stable states for the micelles are found. This bistability is said to be achieved by temperature rise from room temperature up to 55 degrees C. The authors did not find such an internal structural change of the micelle in the experiments. Instead the authors found some large aggregates of the ganglioside in parallel to the micelle caused by the low solubility of this system at room temperature. These aggregates are dissolved quickly with increasing temperature or slowly with time at room temperature. So the variation of the scattering intensity is explainable by dissolving the large particles, meanwhile the structure of the GM1 micelles is the same all the time.

The solution structure of functionally active human proliferating cell nuclear antigen determined by small-angle neutron scattering

The function of proliferating cell nuclear antigen (PCNA) in DNA replication and repair is to form a sliding clamp with replication factor C (RF-C) tethering DNA polymerase delta or epsilon to DNA. In addition, PCNA has been found to interact directly with various proteins involved in cell cycle regulation. The crystal structure of yeast PCNA shows that the protein forms a homotrimeric ring lining a hole through which double-stranded DNA can thread, thus forming a moving platform for DNA synthesis. Human and yeast PCNA are highly conserved at a structural and functional level. We determined the solution structure of functionally active human PCNA by small-angle neutron scattering. Our measurements strongly support a trimeric ring-like structure of functionally active PCNA in solution, and the data are in good agreement with model calculations based on the crystal structure from yeast PCNA. The human PCNA used in the small-angle neutron scattering experiments was active before and after the measurements in a RF-C independent and a RF-C dependent assay suggesting that the trimeric structure is the in vivo functional form.

Effects of reagent and enzymatically generated hypochlorite on physicochemical and metabolic properties of high density lipoproteins

Myeloperoxidase (MPO), a protein secreted by activated phagocytes, may be a potential candidate for the generation of modified/oxidized lipoproteins in vivo via intermediate formation of HOCl, a powerful oxidant. During the present study, the effects of reagent NaOCl and OCl- generated by the MPO/H2O2/Cl- system on physicochemical and metabolic properties of high density lipoprotein (HDL) subclass 3 (HDL3) were investigated. Up to a molar oxidant:lipoprotein ratio of approximately 30:1, apolipoprotein A-I (apoA-I), the major HDL3 apolipoprotein component, represented the preferential target for OCl- attack (consuming 35-76% of the oxidant), thereby protecting HDL3 fatty acids (consuming between 17 and 30% of the oxidant) against OCl--mediated modification. At molar oxidant:HDL3 ratios >/= 60:1, we have observed pronounced consumption of HDL3 unsaturated fatty acids with concomitant formation of fatty acid chlorohydrins. Modification of HDL3 in the presence of the MPO/H2O2/Cl- system resulted in amino acid oxidation in a manner comparable with that found with reagent NaOCl only. Treatment of HDL3 with reagent NaOCl as well as modification by the MPO/H2O2/Cl- system resulted in significantly enhanced turnover rates of HDL3 by mouse peritoneal macrophages, an effect that was not a result of HDL3 aggregation as judged by dynamic and static light-scattering experiments. In comparison with native HDL3, the degradation by macrophages was enhanced by 4- and 15-fold when HDL3 was modified with reagent NaOCl or the MPO/H2O2/Cl- system. Finally, the ability of HDL3 to promote cellular cholesterol efflux from macrophages was significantly diminished after modification with reagent NaOCl. Collectively, these results demonstrate that the modification of HDL3 by hypochlorite (added as reagent or generated by the MPO/H2O2/Cl- system) transformed an antiatherogenic lipoprotein particle into a modified lipoprotein with characteristics similar to lipoproteins commonly thought to initiate foam cell formation in vivo.

Small-Angle Scattering of Interacting Particles. I. Basic Principles of a Global Evaluation Technique

Indirect Fourier transformation is a well established method for the evaluation of small-angle scattering data. This technique, however, is restricted to dilute solutions, as for higher concentrations particle interactions can no longer be neglected. As the scattering intensity contains intra- and interparticle scattering contributions, the evaluation of scattering data is no longer just the solution of a linear weighted least-squares problem because the scattering intensity can, under certain conditions, be written as the product of the particle form factor and the so-called structure factor, which leads to a highly non-linear problem. In this paper a global evaluation technique including the structure factor is presented so that it is possible to determine the form factor and the structure factor simultaneously. This technique can be understood as a generalized version of the indirect Fourier transformation method. Like in the indirect Fourier transformation, there are no models or no analytical restrictions used for the form factor, and the structure factor is parameterized with up to four parameters for a given interaction model. A simultaneous determination of these two functions is possible due to the different analytical behavior of these functions, which also leads in most cases to the existence of a global minimum in the parameter surface. An algorithm to solve this nonlinear least-squares problem has been developed and applied to simulated data for a variety of different uncharged systems.

Characterization of heme-deficient neuronal nitric-oxide synthase reveals a role for heme in subunit dimerization and binding of the amino acid substrate and tetrahydrobiopterin

Neuronal nitric-oxide (NO) synthase contains FAD, FMN, heme, and tetrahydrobiopterin as prosthetic groups and represents a multifunctional oxidoreductase catalyzing oxidation of L-arginine to L-citrulline and NO, reduction of molecular oxygen to superoxide, and electron transfer to cytochromes. To investigate how binding of the prosthetic heme moiety is related to enzyme activities, cofactor, and L-arginine binding, as well as to secondary and quaternary protein structure, we have purified and characterized heme-deficient neuronal NO synthase. The heme-deficient enzyme, which had preserved its cytochrome c reductase activity, contained FAD and FMN, but virtually no tetrahydrobiopterin, and exhibited only marginal NO synthase activity. By means of gel filtration and static light scattering, we demonstrate that the heme-deficient enzyme is a monomer and provide evidence that heme is the sole prosthetic group controlling the quaternary structure of neuronal NO synthase. CD spectroscopy showed that most of the structural elements found in the dimeric holoenzyme were conserved in heme-deficient monomeric NO synthase. However, in spite of being properly folded, the heme-deficient enzyme did bind neither tetrahydrobiopterin nor the substrate analog N(G)-nitro-L-arginine. Our results demonstrate that the prosthetic heme group of neuronal NO synthase is requisite for dimerization of enzyme subunits and for the binding of amino acid substrate and tetrahydrobiopterin.

Physicochemical behavior of the ganglioside GM3 in dilute aqueous solution

The aggregative properties of the ganglioside GM3 have been studied with small-angle X-ray scattering and dynamic light scattering in dilute aqueous solutions. Dynamic light scattering experiments show that GM3 solutions are very polydisperse containing a large amount of small aggregates (hydrodynamic radius of 7-9 nm) in addition to a quite broad distribution of aggregates with an average hydrodynamic radius of 50-60 nm and a small fraction of very large aggregates (> 200 nm). This together with small-angle X-ray scattering scattering experiments and model calculations suggests the coexistence of a lamellar phase (vesicles or extended lamellae) with small aggregates (modelled as lamellar platelets). The latter can also be viewed as lamellar fragments coming from GM3 vesicles which constantly break and reform.

Structural analysis of porcine brain nitric oxide synthase reveals a role for tetrahydrobiopterin and L-arginine in the formation of an SDS-resistant dimer

Nitric oxide synthases (NOSs), which catalyze the formation of the ubiquitous biological messenger molecule nitric oxide, represent unique cytochrome P-450s, containing reductase and mono-oxygenase domains within one polypeptide and requiring tetrahydrobiopterin as cofactor. To investigate whether tetrahydrobiopterin functions as an allosteric effector of NOS, we have analyzed the effect of the pteridine on the conformation of neuronal NOS purified from porcine brain by means of circular dichroism, velocity sedimentation, dynamic light scattering and SDS-polyacrylamide gel electrophoresis. We report for the first time the secondary structure of NOS, showing that the neuronal isozyme contains 30% alpha-helix, 14% antiparallel beta-sheet, 7% parallel beta-sheet, 19% turns and 31% other structures. The secondary structure of neuronal NOS was neither modulated nor stabilized by tetrahydrobiopterin, and the pteridine did not affect the quaternary structure of the protein, which appears to be an elongated homodimer with an axial ratio of approximately 20/1 under native conditions. Low temperature SDS-polyacrylamide gel electrophoresis revealed that tetrahydrobiopterin and L-arginine synergistically convert neuronal NOS into an exceptionally stable, non-covalently linked homodimer surviving in 2% SDS and 5% 2-mercaptoethanol. Ligand-induced formation of an SDS-resistant dimer is unprecedented and suggests a novel role for tetrahydrobiopterin and L-arginine in the allosteric regulation of protein subunit interactions.

Sizing of colloidal particles with light scattering: corrections for beginning multiple scattering

Static light scattering is widely used for sizing of particles with radii in the range of 50 nm up to several micrometers. These experiments usually require very low particle concentrations (<10(-4)) for prevention of multiple scattering. As a consequence, nonabsorbing samples that are suited for light-scattering investigations must be transparent so that the transmittance of the incident light is typically above 95%. Investigations of less translucent samples require corrective terms for the beginning of multiple scattering to retrieve the particle-size distribution successfully. We applied a computationally convenient first-order approximation for the multiple-scattering problem that has Hartel's approach in its first steps. When incorporated into our inversion technique, this approximation functions well for samples with transmittances above 30%. We present examples of applications to experimental data.

Phase behavior of the antineoplastic ether lipid 1-O-octadecyl-2-O-methyl-glycero-3-phosphochloline

The physicochemical properties of the antineoplastic etherphospholipid 1-O-octadecyl-2-O-methyl-glycero-3-phosphochline were examined in the concentration range 1-35% (w/w) lipid, as a function of temperature (range -10 degrees C to 40 degrees C) and of different aqueous solvents by dynamic light scattering, small- and wide-angle X-ray scattering, differential scanning calorimetry and ultrasonic speed measurements. On cooling the lipid dispersion undergoes a phase transition near 6 degrees C, transforming slowly from a micellar into a lamellar gel phase with interdigitating hydrocarbon chains. The lamellar repeat distance is nearly constant over the hydration range 65-90% buffer (d = 5.09-5.14 nm). The size of the micelles in terms of the hydrodynamic radius is 3.8 +/- 0.1 nm, the polydispersity is low. Their average shape is spherical. The electron density distribution across the micelle gives 2.5 nm for the extension of the hydrocarbon chains and 1.5 nm for the polar moiety. The existence of micelles was verified up to a concentration of 35% lipid. Throughout this concentration range size and shape do not change significantly. The kinetics of formation of the low-temperature phase is slow on cooling, increasing with increasing concentration. Upon heating the phase behavior shows a hysteresis. The extended lamellar organizations start to break down into smaller aggregates near 3 degrees C. The micellar phase is reformed near 20 degrees C.

Shape change of human blood platelets: reliable and fast detection by quasi-elastic light scattering

Quasi-elastic light scattering has been used for the first time to obtain reliable information about the morphology of platelets under physiological conditions within a short time. By measuring two independent parameters (electrophoretic mobility and diffusion coefficient) it is possible to distinguish between different stages of shape change on the one hand, and between shape change and binding of particles to the platelet surface without shape change on the other hand.

Optical sizing of small colloidal particles: an optimized regularization technique

Optical particle sizing in the range of 10 nm up to several micrometers by means of quasi-elastic and elastic light scattering requires sophisticated data inversion techniques. We have developed an optimized regularization technique that can be used for the inversion of such light-scattering data. The technique has been successfully tested for a large number of simulated and measured data. It is easy to handle. Typical problems that arise in practical applications are discussed.

Mueller matrix calculations for randomly oriented rotationally symmetric objects with low contrast

Mueller matrices for micrometer-sized objects (2 </= kalpha </= 15) have been calculated for spherical and randomly oriented nonspherical and inhomogeneous bodies with relative refractive indices <1.3. These matrices were found to be highly different from the Rayleigh-Debye matrix as well as from the matrices observed for particles with higher contrast. Some general conclusions have been drawn for homogeneous spherical and nonspherical particles. Layered spheres and spheres with a small imaginary part of the refractive index show some unusual polarization behavior. It was not possible to deduce general features for layered spheres because of their complexity. We found almost invariant Mueller matrices for particles with small absorption in the investigated Mie region.

Information retrieval from X-ray small-angle scattering with polychromatic (`white') synchrotron radiation

The possibilities of obtaining structural information from X-ray small-angle scattering experiments with `white' polychromatic synchrotron radiation using line collimation are investigated by numerical simulation. Theoretical scattering curves of geometrical models were smeared with the appropriate wavelength distributions and slit-length functions, afflicted by statistical noise, and then evaluated by identical methods as normally used for experimental data, as described previously [program ITP; Glatter (1977). J. Appl. Cryst. 10, 415–421]. It is shown that even for a wavelength distribution of 50% half width, the information content is not limited to the parameters derived from the central part of the scattering curves, i.e. the radius of gyration and the zero-angle intensity, but also allows qualitative information on particle shape via the distance distribution function p(r). By a `hinge-bending model' consisting of two cylinders linked together at different angles it is demonstrated that changes in the radius of gyration amounting to less than 5% can be detected and quantified, and the qualitative changes in particle shape be reproduced.