Binding of spin-labeled clofibrate to lipoproteins

The binding of spin-labeled clofibrate to native and partially delipidated lipoproteins is a rapid, linear and non-saturable process observed up to the critical micellar concentration of the drug. Low-density lipoproteins (LDL) display a lower affinity for the drug than very-low-density lipoproteins (VLDL) and high-density lipoproteins (HDL) relative to their respective specific volume. Unlike various lipophilic drugs, uptake of spin-labeled clofibrate does not correlate with lipoprotein lipid volume. Spin-labeled clofibrate binding to LDL is enhanced when the temperature increases above 25 degrees C. The binding to HDL and VLDL is less temperature-sensitive. The simulation of the ESR spectra has shown that two types of motion should be superimposed for the spin-labeled clofibrate in HDL, in LDL or in partially delipidated LDL. From 40 down to 25 degrees C for HDL and LDL, a fast anisotropic motion is observed. From 25 degrees C down to 5 degrees C, a two-component motion takes place, including a slow isotropic motion of the probe tumbling in a highly hydrophobic environment. Interactions of spin-labeled clofibrate with the apolipoproteins in HDL and LDL are assumed from the emergence of this strongly immobilized component observed when the temperature decreases. In contrast, for spin-labeled clofibrate inserted in the apolar core of VLDL, ESR shows only one component in the whole temperature range (5-40 degrees C). The location of the spin-labeled drug inside the various lipoprotein particles is discussed as a function of temperature.     

Binding of plasma low density lipoproteins to erythrocytes

Low density lipoproteins (LDL) containing apolipoprotein B bind to intact, freshly isolated erythrocytes. The LDL-erythrocyte interaction is of low affinity, with a Kd of 1.1 x 10(-6) M. Binding is noncooperative. There are about 200 binding sites per cell and, within the limits of experimental uncertainty, these sites comprise a homogeneous class. Binding of LDL is a temperature-independent process. The maximum amount of LDL blood increases following proteolytic digestion of the cells with trypsin or chymotrypsin. The specificity of the binding sites for LDL is not absolute: high density lipoproteins and lipid vesicles composed of phosphatidylcholine or phosphatidylcholine/cholesterol (equimolar) complete with LDL for occupancy of 60% of the binding sites. Modification of 5--6 of the 9 apolipoprotein B arginine residues with 1,2-cyclohexanedione/borate or of 10--15 of the 20 lysine residues by reductive methylation does not alter the ability of LDL to bind to erythrocytes. Native LDL and methylated-LDL alter erythrocyte morphology. However, LDL in which the arginine residues are derivatized with 1,2-cyclohexanedione/borate do not induce the discocyte leads to echinocyte transformation. Chemically modified and native LDL exchange cholesterol with erythrocytes at equal rates and to nearly equal extents. Taken together, the data suggest that the binding sites for LDL on the erythrocyte membrane are distinct from the LDL receptors at the surface of other cells--e.g., fibroblasts and lymphocytes--which do not bind HDL and which do not recognize LDL with derivatized arginine or lysine residues. It is proposed that the biological function of the erythrocyte binding sites is to mediate the exchange of cholesterol between the cell membrane and lipoproteins.     

Systematic toxicological analysis: computer-assisted identification of poisons in biological materials

A new software was developed to improve the chances for identification of a "general unknown" in complex biological materials. To achieve this goal, the total ion current chromatogram was simplified by filtering the acquired mass spectra via an automated subtraction procedure, which removed mass spectra originating from the sample matrix, as well as interfering substances from the extraction procedure. It could be shown that this tool emphasizes mass spectra of exceptional compounds, and therefore provides the forensic toxicologist with further evidence-even in cases where mass spectral data of the unknown compound are not available in "standard" spectral libraries.     

Binding of 5-methoxypsoralen to human serum low density lipoproteins

5-methoxypsoralen (5-MOP) binds to human serum low density lipoproteins (LDL) according to a two-step process. Scatchard analysis of the first step yields K = 1.4 × 10⁵ M^?1 and 4 binding sites. It involves the LDL apoprotein. The second step corresponds to a solubilization, in the lipidic core, of ? 45 molecules of 5MOP per LDL molecule. It is accompanied by a large blue shift of the 5MOP fluorescence. The ability of LDL to bind 5MOP and to carry it into various cells may explain some biological effects sometimes encountered during PUVA therapy.     

Binding of low density lipoproteins (LDL) to platelets

Binding of LDL to platelets was studied by two independent methods, radioactive and flow cytofluorimetry, using 125I- and fluorescently labelled RITC-LDL. Saturation of 125I- and RITC-LDL binding to platelets, inhibition of binding by unlabelled LDL and a lower inhibitory effect of unlabelled HDL evidence the existence of a limited number of binding sites specific for LDL in platelets. Unlike nuclear cells platelets do not degrade LDL. The binding of LDL to platelets is reversible and independent of Ca2+. The decrease of total binding level at 4 degrees and the absence of heparin effect on the release of bound LDL suggest LDL incorporation into platelets.     

Binding of an inert, cationic osmium probe to walls of Bacillus subtilis.

X-ray fluorescence spectroscopy and electron microscopy of unstained specimens have been used to study the binding of chloropentaammineosmium(III) chloride to isolated walls of Bacillus subtilis. Native walls bound 0.220 mumol of the osmium probe per mg (dry weight) of walls, whereas walls which were chemically treated to neutralize the available carboxylate groups of the peptidoglycan bound only 0.040 mumol. Teichoic acid-depleted walls bound 0.210 mumol. Thin sections of all wall types showed the osmium probe to be scattered throughout the wall matrix as a small staining deposit. The results support the idea that the metal ion-binding capacity of these walls is mediated by the available carboxylate groups in the wall fabric.     

Binding properties of high-density lipoprotein subfractions and low-density lipoproteins to rabbit hepatocytes

Primary cultures of rabbit hepatocytes which were preincubated for 20 h in a medium containing lipoprotein-deficient serum subsequently bound, internalized and degraded 125I-labeled high-density lipoproteins2 (HDL2). The rate of degradation of HDL2 was constant in incubations from 3 to 25 h. As the concentration of HDL2 in the incubation medium was increased, binding reached saturation. At 37 degrees C, half-maximal binding (Km) was achieved at a concentration of 7.3 micrograms of HDL2 protein/ml (4.06 X 10(-8)M) and the maximum amount bound was 476 ng of HDL2 protein/mg of cell protein. At 4 degrees C, HDL2 had a Km of 18.6 micrograms protein/ml (1.03 X 10(-7)M). Unlabeled low-density lipoproteins (LDL) inhibited only at low concentrations of 125I-labeled HDL2. Quantification of 125I-labeled HDL2 binding to a specific receptor (based on incubation of cells at 4 degrees C with and without a 50-fold excess of unlabeled HDL) yielded a dissociation constant of 1.45 X 10(-7)M. Excess HDL2 inhibited the binding of both 125I-labeled HDL2 and 125I-labeled HDL3, but excess HDL3 did not affect the binding of 125I-labeled HDL3. Preincubation of hepatocytes in the presence of HDL resulted in only a 40% reduction in specific HDL2 receptors, whereas preincubation with LDL largely suppressed LDL receptors. HDL2 and LDL from control and hypercholesterolemic rabbits inhibited the degradation of 125I-labeled HDL2, but HDL3 did not. Treatment of HDL2 and LDL with cyclohexanedione eliminated their capacity to inhibit 125I-labeled HDL2 degradation, suggesting that apolipoprotein E plays a critical role in triggering the degradative process. The effect of incubation with HDL on subsequent 125I-labeled LDL binding was time-dependent: a 20 h preincubation with HDL reduced the amount of 125I-labeled LDL binding by 40%; there was a similar effect on LDL bound in 6 h but not on LDL bound in 3 h. The binding of 125I-labeled LDL to isolated liver cellular membranes demonstrated saturation kinetics at 4 degrees C and was inhibited by EDTA or excess LDL. The binding of 125I-labeled HDL2 was much lower than that of 125I-labeled LDL and was less inhibited by unlabeled lipoproteins. The binding of 125I-labeled HDL3 was not inhibited by any unlabeled lipoproteins. EDTA did not affect the binding of either HDL2 or HDL3 to isolated liver membranes. Hepatocytes incubated with [2-14C]acetate in the absence of lipoproteins incorporated more label into cellular cholesterol, nonsaponifiable lipids and total cellular lipid than hepatocytes incubated with [2-14C]acetate in the presence of any lipoprotein fraction. However, the level of 14C-labeled lipids released into the medium was higher in the presence of medium lipoproteins, indicating that the effect of those lipoproteins was on the rate of release of cellular lipids rather than on the rate of synthesis.     

Improvement of methane biofiltration by the addition of non-ionic surfactants to biofilters packed with inert materials

The effect of non-ionic surfactants on the biofiltration of methane (CH₄) was analyzed. Two biofilters (BF) treating CH₄ were operated for one year at fixed CH₄ concentration of 4.8 g m⁻³ and air flow rate of 0.25 m⁻³ h⁻¹. Three polyoxyethylenes (Brijs), and 3 mono polyoxyethylenesorbitans (Tweens) were added to the nutrient solution at a concentration of 0.5% (w/w). Without surfactant, CH₄ conversion had an average level of 35%, with Brijs the CH₄ conversion varied between 38% and 46%, and with Tweens between 43% and 48%. The non-ionic surfactants decreased the biomass accumulation in the packed bed due to their detergent character. Biofilters were operated in a range of nitrogen concentration in the nutrient solution from 0.5 to 2 gN L⁻¹ using Tween 20 at a concentration of 0.5% (w/w). The EC_max observed in this study, 45 g m⁻³ h⁻¹, occurred when the nitrogen concentration was 1 gN L⁻¹.     

Binding of high-density lipoproteins to luteal membranes: the role of prolactin, luteinizing hormone, and circulating lipoproteins

Ovarian and adrenal membranes from immature gonadotropin-primed rats, treated with 4-amino-pyrazolopyrimidine (4APP) to reduce endogenous lipoprotein levels, displayed higher binding of porcine high-density lipoprotein (HDL) when compared to control rats. Immature, hypophysectomized (HYPOX) rats bearing corpora lutea (CL) on Day 5 after ovulation had lower levels of serum progesterone and reduced capacity for HDL and human chorionic gonadotropin (hCG) binding to ovarian membranes when compared with intact animals. Hypophysectomy also reduced the number of HDL binding sites in adrenal membranes. Treatment of HYPOX animals with luteinizing hormone (LH) and prolactin (Prl) alone or in combination increased the HDL binding sites in the ovary relative to HYPOX-untreated rats. Neither hormone affected binding to adrenals, where only adrenocorticotropic hormone (ACTH) enhanced HDL binding. LH treatment reduced the serum progesterone levels and hCG binding to the ovaries, whereas Prl administration increased progesterone levels with no effect on hCG binding. We conclude from this study that HDL binding in the luteinized ovary is regulated by Prl and LH and circulating lipoproteins, whereas in adrenals it is regulated by ACTH and circulating levels of lipoproteins.     

Binding affinity and reactivity of lecithin cholesterol acyltransferase with native lipoproteins.

The first step in the reaction of lecithin cholesterol acyltransferase (LCAT) with lipoproteins is the interfacial binding of the enzyme to the lipid surfaces. In this study the equilibrium dissociation constants (Kds) for the interaction of pure human plasma LCAT with LDL, HDL2, HDL3, and a reconstituted discoidal HDL (rHDL) were determined by the activity-inhibition method. In addition, enzyme kinetics were measured with each of the lipoprotein substrates. Based on phospholipid concentrations, the Kd values (0.9 x 10(-5) to 4.6 x 10(-5) M) increased in the order rHDL = HDL3 相似文献   

Binding of bovine follicular fluid glycosaminoglycans to fibronectin, laminin and low-density lipoproteins

Interactions of bovine follicular fluid glycosaminoglycans (GAGs) with extracellular matrix (ECM) components fibronectin and laminin and with low-density lipoproteins (LDL) were examined using affinity chromatography. Glycosaminoglycans from small (diameter less than 5 mm) and large (diameter 11-20 mm) follicles were isolated from follicular fluid. The dermatan sulphate or heparan sulphate from small or large follicles was applied to Fn-, Lm- or LDL-Sepharose columns. Portions of each fraction of the bound or unbound GAG were then subjected to gel filtration h.p.l.c. for quantification. The binding interaction between dermatan sulphate and fibronectin was significantly greater than between heparan sulphate and fibronectin (P less than 0.05); the binding interaction between GAGs from small follicles and fibronectin was significantly greater than between GAGs from large follicles (P less than 0.05). The binding interaction between GAGs from small follicles and laminin was significantly greater than for GAGs from large follicles (P less than 0.05). Dermatan sulphate from small follicles bound to fibronectin (42%), laminin (36%) and LDL (14%) and that from large follicles bound to fibronectin (14%), laminin (23%) and LDL (14%). Heparan sulphate from small follicles bound to fibronectin (17%), laminin (15%) and that from large follicles bound to fibronectin (13%), laminin (10%) and LDL (6%). These results suggest that dermatan sulphate, but not heparan sulphate, from follicles at different stages of development exhibit a varied ability to interact with components of the ECM. Both substances bound to LDL comparably in small amounts.     

Binding of lipopolysaccharide and complexes of lipopolysaccharide to serum low density lipoproteins to liver macrophages

Binding of [³H]-lipopolysaccharide toxin (LPS) and complexes of LPS with serum [¹²⁵I]-labeled low density lipoproteins (LDL) to primary culture of rat liver macrophages (Kupffer cells) has been studied. Total, specific and nonspecific binding was determined. The receptor interaction was shown to dominate for both LPS and LDL-LPS complexes, representing 70–77% and 80–85%, respectively. The Scatchard plot was essentially non-linear for LPS binding but linear for the LDL-LPS complexes. At the Scatchard graph of LPS binding, however, two regions approximately fitting the linear regression could be identified. These regions correspond to two different types of specific binding sites: the first is for lower toxin concentrations of 0.25–0.50 μg/ml with K _d = 0.75 μg/ml; while the second is for higher LPS concentrations of 7.5–15 μg/ml with K _d = 5.39 μg/ml. For LDL-LPS complexes only K _d of 2.80 μg/ml was obtained. The LDL-LPS complexes significantly blocked the LPS binding (?40%) while acetylated or oxidized LDLs exerted a less pronounced effect. LPS inhibited binding of LDL-LPS complexes (?60%), while acetylated or oxidized LDLs suppressed interaction of LDL-LPS complexes with Kupffer cells insignificantly. It is suggested that, while binding to the Kupffer cell surface, a substantial portion of both LPS and LDL-LPS complexes share the same scavenger receptors with which, however, modified LDLs interact weakly. The LDL-LPS complexes can interact, apart from receptors common with LPS, with other receptors exhibiting similar binding parameters, with the apo-B/E receptors playing an inessential role.     

Binding of divalent cations with low density lipoproteins. A study by ESR

The binding of bivalent metal ions Cu2+, Zn2+, Ca2+, Mg2+ to low-density lipoproteins (LDL) was investigated by the ESR technique. The monitoring of ESR spectra of paramagnetic Mn2+ ions in the presence of above-listed cations made it possible to evaluate the dissociation constants of their complexes with LDL. The effective dissociation constant of the complex Mn(2+)-LDL used for calculations was KD = (1.1 +/- 0.4) x 10(-4) M according to literature data. The investigated cations may be classified into two groups: 1) low dissociation constants were characteristic for Cu2+ ions [KD = (1.3 +/- 0.5) x 10(-4) M], which demonstrated a high oxidative ability, and for Zn2+ [KD = (0.95 +/- 0.45) x 10(-4) M] and Mn2+ ions, which could strongly influence the copper-induced LDL oxidation; 2) Ca2+ and Mg2+ were characterized by higher values of KD [(6 +/- 1) x 10(-4) M and (7.5 +/- 1.5) x 10(-4) M, accordingly] and slightly affected the Cu(2+)-induced oxidation of LDL. The results of the present work reinforced our earlier conjecture that cations may influence the process of lipid peroxidation, binding only to particular binding sites on the surface of LDL.     

Binding of unmodified low-density lipoproteins to human fibroblasts. An investigation by immunoelectron microscopy

The binding of unmodified low density lipoproteins to the plasma membrane of fibroblasts was studied at the ultrastructural level. The bound low density lipoprotein was visualized by an indirect immunoperoxidase technique, with the use of an antiserum against apoprotein B. Immunoreactive regions representing bound apoprotein B were found on the plasma membrane, in indented regions with a diameter of 0.15–0.30 μm and a fuzzy coat on the cytoplasmic side. Fibroblasts from a patient homozygous for hyperlipoproteinaemia type IIa showed no immunoreactive material in the indented regions. The specific ¹²⁵I-labelled low density lipoprotein binding to these homozygous fibroblasts was 7% compared to control fibroblasts.     

Binding of unmodified low-density lipoproteins to human fibroblasts. An investigation by immunoelectron microscopy.

The bindinf of unmodified low density lipoproteins to the plasma membrane of fibroblasts was studied at the ultrastructural level. The bound low density lipoprotein was visualized by an indirect immunoperoxidase technique, with the use of an antiserum against apoprotein B. Immunoreactive regions representing bound apoprotein B were found on the plasma membrane, in indented regions with a diameter of 0.15--0.30 micrometer and a fuzzy coat on the cytoplasmic side. Fibroblasts from a patient homozygous for hyperlipoproteinaemia type IIa showed no immunoreactive material in the indented regions. The specific 125I-labelled low density lipoprotein binding to these homozygous fibroblasts was 7% compared to control fibroblasts.     

Semiautomated computer-assisted image analysis to quantify 3,3'-diaminobenzidine tetrahydrochloride-immunostained small tissues

This work aimed to develop a technique to measure stained areas in images from sample tissue sections, namely when the structure of interest does not fill the entire image field of the microscope. We propose a semiautomated computer-assisted image analysis (SACAIA) method in which brightfield color images of 3,3'-diaminobenzidene tetrahydrochloride (DAB)-stained antigens are converted to their blue component and boundaries are delineated to extract the object of interest. The number of pixels of a defined color (elicited by DAB) is counted and used to measure the stained area relative to the total area of the tissue under study. The percentages of area stained with adenosine A(1) receptor were 40.76+/-2.08 and 42.44+/-2.26% for manual analysis and SACAIA, respectively (P=0.582). A strong linear correlation of A(1) receptor quantification was found (r=0.98, P<0.001, and 95% CI=0.97 to 0.99 for manual method; r=0.99, P<0.001, and 95% CI=0.98 to 0.99 for SACAIA method). The extent to which misclassification affected staining quantification was evaluated by Bland-Altman analysis, indicating that this method can be applied accurately to quantify the immunohistochemical staining area (occupied by a specific antigen) in small sample tissues that do not fill the entire image field of the microscope.     

Binding of high density lipoproteins to cell receptors promotes translocation of cholesterol from intracellular membranes to the cell surface

Cultured cells have on their cell surface a specific high-affinity binding site (receptor) for high density lipoproteins (HDL) which appears to promote cholesterol efflux. In this study we characterized the cellular mechanisms involved in HDL receptor-mediated transport of cholesterol from cultured human fibroblasts and bovine aortic endothelial cells. HDL3, chemically modified by tetranitromethane (TNM-HDL3), is not recognized by this receptor and was used as a control for efflux not mediated by HDL receptor binding. HDL3 and TNM-HDL3 were found to be equally effective in causing efflux of plasma membrane cholesterol radiolabeled with [3H]cholesterol. However, HDL3 was much more effective than TNM-HDL3 in causing efflux of [3H]cholesterol associated with intracellular membranes. By measuring movement of endogenously synthesized [3H]cholesterol to the plasma membrane, and into the medium, we found that HDL3 induced a rapid movement of [3H]cholesterol from a preplasma membrane compartment to the plasma membrane that preceded [3H]cholesterol efflux. This effect was not observed with TNM-HDL3. Thus, receptor binding of HDL3 appears to facilitate removal of cellular cholesterol from specific intracellular pools by initiation of translocation of intracellular cholesterol to the plasma membrane.