Fractions Of Different Densities Research Articles

Individual contributions to the overall microelement concentrations in coal

The microelement concentrations in coal represent the sum of contributions from the organic mass, the mineral impurities, and the initial plant matter. These contributions are mutually independent and may differ very considerably. Generally, the microelement concentrations in coal are determined by their content in the organic mass. Identification of the individual contributions to the overall microelement concentrations in coal is of interest in assessing the rare-metal content of coal and means of extracting microelements. Unsatisfactory and often conflicting results are obtained by existing methods of identifying those contributions (by separation of the coal into fractions of different density; by comparison with the abundance ratios in the aleuropelite fraction; by correlation with the ash content). A method is proposed for statistical resolution of the individual contributions to the overall microelement concentrations in coal.

Depositional Processes of Organic Matter in the Rhône River Delta (Gulf of Lions, France) Traced by Density Fractionation Coupled with Δ14C and δ13C

As a main source of freshwater and particles, the Rhône River plays a major role in the biogeochemical cycle of organic carbon (OC) in the Mediterranean Sea. To better understand the origin of organic matter and the processes leading to its export to the coastal sea near the Rhône River, we measured radiocarbon (Δ14C) and stable carbon isotopes (δ13C) in the sediments of the delta, after density fractionation. In April 2007, 3 sites located along an offshore transect (A, C, and E) were sampled for surface sediments, and bulk sediment was separated into 4 fractions of different densities (<1.6, 1.6–2, 2–2.5, and >2.5 g cm−3). In order to better understand the evolution of the OC along the transect, we investigated the OC sources and their evolution for each density fraction. Bulk OC shows a large increase in δ13C from −27.2′ nearshore to −24.5′ at offshore stations while Δ14C decreased from 59′ to −320′. The distribution of δ13C with density displayed a convex pattern at all stations. Except for fraction >2.5 g cm−3, δ13C increases by 2.5′ between stations A and E, indicating a loss of terrestrial signature. The distribution of Δ14C versus density had a concave pattern at all stations: at a single station, it showed a large heterogeneity with a difference of 500–600′ between the <1.6 and 2–2.5 g cm−3 fractions. A decrease in Δ14C of −400′ among the different density fractions was observed along the offshore transect. The density fraction >2.5 g cm−3 had less variability, with an average δ13C of −24.6 ± 0.4′ and Δ14C of −370 ± 115′. Several processes may explain this distribution: retention in the prodelta of large particles; mineralization of all fractions during the transport and deposition in the delta and shelf sediments; and dilution of terrestrial particles in continental shelf pool.

Sodium–calcium exchanger and lipid rafts in pig coronary artery smooth muscle

Pig coronary artery smooth muscle expresses, among many other proteins, Na+–Ca2+-exchanger NCX1 and sarcoplasmic reticulum Ca2+ pump SERCA2. NCX1 has been proposed to play a role in refilling the sarcoplasmic reticulum Ca2+ pool suggesting a functional linkage between the two proteins. We hypothesized that this functional linkage may require close apposition of SERCA2 and NCX1 involving regions of plasma membrane like lipid rafts. Lipid rafts are specialized membrane microdomains that appear as platforms to co-localize proteins. To determine the distribution of NCX1, SERCA2 and lipid rafts, we isolated microsomes from the smooth muscle tissue, treated them with non-ionic detergent and obtained fractions of different densities by sucrose density gradient centrifugal flotation. We examined the distribution of NCX1; SERCA2; non-lipid raft plasma membrane marker transferrin receptor protein; lipid raft markers caveolin-1, flotillin-2, prion protein, GM1-gangliosides and cholesterol; and cytoskeletal markers clathrin, actin and myosin. Distribution of markers identified two subsets of lipid rafts that differ in their components. One subset is rich in caveolin-1 and flotillin-2 and the other in GM1-gangliosides, prion protein and cholesterol. NCX1 distribution correlated strongly with SERCA2, caveolin-1 and flotillin-2, less strongly with the other membrane markers and negatively with the cytoskeletal markers. These experiments were repeated with a non-detergent method of treating microsomes with sonication at high pH and similar results were obtained. These observations are consistent with the observed functional linkage between NCX1 and SERCA2 and suggest a role for NCX1 in supplying Ca2+ for refilling the sarcoplasmic reticulum.

Thermochemical properties of coal fractions of different density: A review

Research is reviewed regarding the composition and thermochemical properties of coal fractions of different density. The properties discussed are the thermogravimetric parameters; the free-swelling index; the plastic-layer thickness; the dilatometric characteristics; the yield of fluid (mobile) components of the plastic mass. These properties are determined by the petrographic (maceral) composition of the fractions. With increase in density of the fractions, the liptinite and vitrinite content declines, while the inertinite content grows. Consequently, the chemical structure becomes less aliphatic and more aromatic, with corresponding deterioration in thermochemical properties of the fractions. The results show that fractionation of the coal prior to processing is potentially very effective.

2D-NMR reveals different populations of exposed lysine residues in the apoB-100 protein of electronegative and electropositive fractions of LDL particles

Several potentially atherogenic LDL subfractions present low affinity for the LDL receptor, which result in impaired plasma clearance. Electronegative LDL [LDL(-)] is one of these minor subfractions and the molecular basis for its reduced receptor affinity is not well understood. In the present study, high-resolution 2D-NMR spectroscopy has been employed to characterize the surface-exposed lysine residues of the apolipoprotein (apo)B-100 protein in both LDL(-) and LDL(+) subfractions. LDL(+) showed two populations of lysine residues, similar to those previously described in total LDL. "Normal" Lys have a pk(a) of 10.4 whereas "active" Lys have a pk(a) of 8.8 and have been suggested to be involved in receptor binding. In contrast to LDL(+), the LDL(-) subfraction presented a third type of Lys, named as "intermediate" Lys, with a different microenvironment and higher basicity (pk(a) 10.7). These intermediate Lys cannot be reliably identified by 1D-NMR. Because the abundance of normal Lys is similar in LDL(+) and LDL(-), the intermediate Lys in the apoB-100 molecule of LDL(-) should come from a group of active Lys in LDL(+) particles that have a less basic microenvironment in the LDL(-) particle. These differences between LDL(+) and LDL(-) are indicative of a distinct conformation of apoB-100 that could be related to loss of affinity of LDL(-) for the LDL receptor.

Correlation between the Roga index and the free-swelling index of coal

Literature data on the properties of fractions of different density obtained by liquid centrifuging of metamorphic coal reveal the relation between the Roga index RI and the free-swelling index SI, which describe different aspects of clinkering. A correlation is obtained between RI and SI, whose characteristics depend on the metamorphic stage of the coal. The results suggest that RI should be replaced by SI in dividing coal with a plastic-layer thickness y < 6 mm (D, SS, and TS coal) into subgroups, within the framework of the unified coal classification (State Standard GOST 25543-88).

Hemolymph ionic regulation and adjustments in gill (Na +, K +)-ATPase activity during salinity acclimation in the swimming crab Callinectes ornatus (Decapoda, Brachyura)

We evaluate hemolymph osmotic and ionic regulatory abilities and characterize a posterior gill microsomal (Na +, K +)-ATPase from the marine swimming crab, Callinectes ornatus, acclimated to 21‰ or 33‰ salinity. C. ornatus is isosmotic after acclimation to 21‰ but is hyposmotic at 33‰ salinity; hemolymph ions do not recover initial levels on acclimation to 21‰ salinity but are anisoionic compared to ambient concentrations, revealing modest regulatory ability. NH 4 + modulates enzyme affinity for K +, which increases 187-fold in crabs acclimated to 33‰ salinity. The (Na +, K +)-ATPase redistributes into membrane fractions of different densities, suggesting that altered membrane composition results from salinity acclimation. ATP was hydrolyzed at maximum rates of 182.6 ± 7.1 nmol Pi min − 1 mg − 1 (21‰) and 76.2 ± 3.5 nmol Pi min − 1 mg − 1 (33‰), with little change in K M values (≈ 50 µmol L − 1 ). K + together with NH 4 + synergistically stimulated activity to maximum rates of ≈ 240 nmol Pi min − 1 mg − 1 . K I values for ouabain inhibition (≈ 110 µmol L − 1 ) decreased to 44.9 ± 1.0 µmol L − 1 (21‰) and 28.8 ± 1.3 µmol L − 1 (33‰) in the presence of both K + and NH 4 +. Assays employing various inhibitors suggest the presence of mitochondrial F 0F 1-, and K +- and V-ATPase activities in the gill microsomes.

Molecular Fractionation of Starch in Nycodenz-Dimethyl Sulfoxide by Density-Gradient Ultracentrifugation

Starches from various origins (normal corn, waxy corn, high-amylose corn, normal rice, waxy rice, potato and tapioca) were fractionated by density-gradient ultracentrifugation at 124,000 × g, using a gradient of Nycodenz (0-40%, w/w) in 90% dimethyl sulfoxide (DMSO). The fractions of different densities were collected from a centrifuge tube, and then analyzed by the phenol-sulfuric acid method and iodine-binding test. Amylose and amylopectin were clearly separated by the density-gradient centrifugation within 6 h of centrifugation in the total carbohydrate vs. density profile. The amylose content in the starches, measured from the centrifugation for 6 h, agreed with the values reported in the literature, and the content of intermediate fraction (5-13%) was also measured. Amylopectin quickly reached a density region (1.22-1.23 g/mL) with a sharp and stable peak, whereas amylose showed a band in a broad density range, moving toward higher density as the centrifugation continued. The buoyant density of amylose became similar to that of amylopectin after extensive centrifugation. Because the sedimentation rate of amylose was much lower than that of amylopectin, both starch chains are effectively fractionated in the gradient medium, and the iodine-binding property of the fractionated starches provides valuable information on the chain conformation of starch.

Determining isotopic life history trajectories using bone density fractionation and stable isotope measurements: a new approach.

A number of recent studies have attempted to trace diet at different stages of an individual's life by comparing isotope ratios of bone from different gross anatomical sites within the skeleton. In this study we develop this approach further by separating bone of differing mineral densities within one skeletal element, where each density fraction represents a different period of time. Isotope ratios are measured for these fractions. Each density fraction represents a period of bone formation and maturation, where younger (more recently formed) bone is less well-mineralized and therefore less dense than relatively older packets of bone. In an adult, bone is therefore able to partition approximately the last 15 years of life. Bone fractions were recovered by stepped ultracentrifugation in a series of organic solvents of increasing density, and then collagen was recovered by decalcification in dilute acid, and stable carbon isotope ratios ((13)C/(12)C) were measured. Bone density microstructure was checked for bacterial remodelling using backscattered electron imaging in a scanning electron microscope. Our results indicate that the bone density fractionation method is applicable to archaeological material, here extending to a maximum of 5,000 years BP, and that collagen can successfully be extracted from such fractions. The carbon isotope values for bone fractions of different densities patterned out as expected in one modern control bone and in specimens from five archaeological human skeletons, including three precolonial hunter-gatherers and two 18th/19th century individuals. The latter two are known (from previous assessments) to have undergone marked changes in diet during their lifetimes. Postmortem alteration was evident in some of the specimens examined. The bone density fractionation approach has allowed greater resolution of diet than has hitherto been possible and has provided access to the elusive last years and months of an individual's life.

Plane waves in a heavy two-layer liquid excited by a cylinder moving at an angle to the horizontal

A solution of an initial-boundary-value problem for a system of integrodifferential equations which describes the plane waves excited in an initially stationary heavy two-layer ideal fluid by a cylinder moving at an angle to the horizontal is investigated. The homogeneous fluid fractions of different densities are assumed to be separated by an evolving fluid interface (horizontal plane, if the liquid is at rest). An approximate solution of two problems for the waves excited by a cylinder moving with a constant acceleration and an oscillating cylinder is constructed analytically.

Invasion and growth of Plasmodium falciparum is inhibited in fractionated thalassaemic erythrocytes

Epidemiological and clinical studies have indicated that the thalassaemias may confer protection against malaria. The study reported here investigated this protective effect in vitro, using a new approach which controls for the potential effect of red cell size and age on the virulence of the parasite. A Percoll ™ density gradient method was used to separate α- and β-thalassaemic trait, haemoglobin H and normal red blood cells (RBC) into fractions of different density. Correlations between RBC density, age and size in fractions of all genotypes were established using red cell creatine as an index of cell age. The development of Plasmodium falciparum over 3 erythrocytic cycles (144 h) in whole blood as well as fractionated samples was monitored by slide microscopy and flow cytometry. A significantly reduced rate of parasite invasion and growth was demonstrated in RBC from all thalassaemic genotypes tested. Poor reinvasion rates were noted in the second and third cycles. Increased duration of culture and red cell age also had a greater negative impact on parasite growth in thalassaemic RBC. This poor growth rate was also associated with the arrest of parasite growth at the schizont stage (schizont maturation arrest) and the accumulation of abnormal, trophozoite/schizont stage parasites in the older thalassaemic RBC fractions. These findings suggest a defect in the number and viability of merozoites generated by parasites growing in thalassaemic RBC. Age related factors such as oxidant stress may play a key role in mediating this kind of protective mechanism and deserve further investigation.

Interleukin-3 and lipopolysaccharide interact to inhibit proliferation of mouse bone marrow cells

The mechanisms underlying the multiple biological activities presented by interleukin-3 (IL-3) are not yet fully understood. As a regulator of hematopoiesis, IL-3 is known to interact with several other molecules. The present study investigates the interaction of IL-3 and Escherichia coli lipopolysaccharide (LPS), which results in the inhibition of the in vitro proliferation of mouse bone marrow (BM) cells. BM cells from adult BALB/c mice were cultured at 37°C, with 5% CO 2 in air, in RPMI-1640 medium complemented with fetal calf serum. Viable cells were counted on day 3. Whereas IL-3 and LPS alone increased the number of viable cells as compared to control cultures, the simultaneous addition of the factors lowered that number below controls. Cell fractions of different densities, isolated by Percoll gradient (70, 50 and 40%), also behaved in the same way. The same effect was observed when BM non-adherent cells were isolated 1 day after initiation of cultures and analyzed 2 days later, but not if the culture was initiated in the absence of adherent cells. Pre-incubation experiments showed that only if total BM cells were pre-incubated for 24 h with IL-3/LPS or LPS alone was the inhibitory effect of the two factors maintained. Soluble inhibitory factors were only observed in cultures of adherent BM cells.

Fourier transform infrared spectroscopic study of the carbonate ions in bone mineral during aging

The environment of CO3(2-) ions in the bone mineral of chickens of different ages and in bone fractions of different density have been investigated by resolution-enhanced Fourier Transform Infrared (FTIR) Spectroscopy. Three carbonate bands appear in the upsilon 2 CO3 domain at 878, 871, and 866 cm-1, which may be assigned to three different locations of the ion in the mineral: in monovalent anionic sites of the apatitic structure (878 cm-1), in trivalent anionic sites (871 cm-1), and in unstable location (866 cm-1) probably in perturbed regions of the crystals. The distribution of the carbonate ions among these locations was estimated by comparing the intensities of the corresponding FTIR spectral bands. The intensity ratio of the 878 and 871 cm-1 bands remains remarkably constant in whole bone as well as in the fractions obtained by density centrifugation. On the contrary, the intensity ratio of the 866 cm-1 to the 871 cm-1 band was found to vary directly and decreased with the age of the animal. In bone of the same age, the relative content of the unstable carbonate ion was found to be highest in the most abundant density centrifugation fraction. A resolution factor of the CO3(2-) band (CO3 RF) was calculated from the FTIR spectra which was shown to be very sensitive to the degree of crystallinity of the mineral. The crystallinity was found to improve rapidly with the age of the animal. The CO3 RF in the bone samples obtained by density centrifugation from bone of the same animal was found to be essentially constant.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics and Functional Properties of Red Cells during the First Days of Life

In order to evaluate postnatal red blood cell (RBC) properties and whole-blood rheology, 36 healthy full-term newborn infants were tested twice (cord blood, 4th-day blood) for whole-blood flow rate, hematocrit, hemoglobin (Hb), RBC count, mean corpuscular volume, mean corpuscular Hb and its concentration, white blood cell and platelet count, plasma fibrinogen, erythrocyte glucose-6-phosphate dehydrogenase, glutathione peroxidase (GSH-Px), glutathione reductase, catalase and superoxide dismutase. Another 38 healthy full-term newborns were tested twice for separation of erythrocytes into fractions of different density. Healthy adults were taken as control. The results showed a decreased whole-blood flow rate in blood drawn on the 4th day with respect to cord blood. A multivariate analysis with flow rate as dependent variable demonstrated a significant positive correlation with GSH-Px on the 4th day. The assays of RBC densities showed a significant increase in the first 4 days.

B cell-stimulating activity of lymphoid cell membrane fractions.

We had previously found that a mutagenized subline of the mouse thymoma EL4 very efficiently stimulates B cells via direct cell-cell contact, thereby inducing the responsiveness of B cells to cytokines. In the present study, we investigated whether this effect could also be mediated by plasma membranes of EL4 (and other) cells. By equilibrium centrifugation of cell homogenates, four cell membrane fractions of different densities were obtained. These were tested for (a) stimulation of B cell proliferation in conjunction with EL4 supernatant as source of cytokines, and (b) enhancement of B cell proliferation at suboptimal concentration of lipopolysaccharide. It turned out that all membrane fractions from a variety of T lineage cells (mutant EL4, parent EL4, BW5147, P198 thymomas, normal T cells) and B lineage cells (BCL1 lymphoma, X63Ag8 cytoplasma, normal B cells) exhibited similar B cell stimulating activity in both assays. Interleukin 1 activity was not detected in the membrane fractions. Heat treatment abolished all activity showing that protein at least was involved. Either protease treatment or extraction with detergent abolished the activity of subcellular fractions rich in intracellular membranes but not that of fractions most enriched in surface membranes. Finally, erythrocyte membranes also displayed B cell-stimulating activity sensitive to protease and detergent extraction. In contrast, and in confirmation of a previous study, liver cell membrane was inhibitory in the B cell proliferation assay with lipopolysaccharide. In conclusion, the effects of cell membranes did not reflect the unique activity of intact mutant EL4 cells. However, with respect to our data it is conceivable that membrane proteins with relatively nonspecific activity and wide distribution among lymphoid cells could play a role in T cell help together with molecules specialized in cell adhesion and cell triggering.

Isolation of transverse tubules by fractionation of sarcoplasmic reticulum preparations in ion-free sucrose density gradients

A new method for the preparation of transverse tubules (T-tubules) from rabbit skeletal muscles is reported. When crude sarcoplasmic reticulum (SR) preparations were centrifuged on sucrose density gradients containing buffering ions (buffered gradients) 70–80% of the material sedimented as a single heavy band in the region of 43% sucrose. When this fraction (or crude SR) was recentrifuged on sucrose gradients prepared free of buffer or other ions (ion-free gradients) the heavy band dissociated into three fractions of different densities. The lightest fraction sedimented at 28% sucrose and was identified as T-tubules on the basis of its nitrendipine and ouabain binding properties. The enzymatic properties, cholesterol contents, and protein compositions of the fractions obtained when SR is centrifuged on buffered and ion-free sucrose density gradients were measured. The T-tubules were enriched in cholesterol and in marker enzymes for surface membranes while the other fractions were shown to be terminal cisternae and longitudinal cisternae on the basis of their (Ca 2+,Mg 2+)-ATPase activities and characteristic protein profiles.

Density gradient analysis of secretions produced in vitro by human and canine airway mucosa: identification of lipids and proteoglycans in such secretions.

Human and canine airway mucosal explants synthesize and secrete high molecular weight glycoconjugates, incorporating 14C-glucosamine, a radioactive precursor to epithelial glycoprotein. Our examination of secretions produced by several individual specimens, however, did not reveal epithelial glycoprotein of typical buoyant density (1.5 g/ml in CsBr); only a high-density component with features of glycoprotein and proteoglycan. To provide sufficient material for characterization, secretions from several specimens of human and canine explants were separately pooled and subjected to DGU in CsBr. After removal of lipids and proteins, the glycoconjugates were recovered into five fractions of different density. 14C-glucosamine had been incorporated in all five fractions. Fractions 1-4 together accounted for 88% of the radiolabel but gas chromatography indicated that none of these contained epithelial glycoprotein. Their amino acid compositions were similar to those of proteoglycans and electrophoresis confirmed the presence of chondroitin sulfates A, B, C, heparan sulfate and hyaluronic acid. Sugars typical of epithelial glycoprotein were identified only in the glycoconjugate subfraction 5 of lowest density (and also lowest in yield) in which glycosaminoglycans were also identified. By addition of radioactive precursors, 14C acetate, 14C palmitate and 14C mevalonic acid to the culture medium and autoradiography of the secreted lipids we have shown that the tracheal explants actively synthesize lipids. Lipids accounted for a high proportion, almost half by weight, of the explant secretion. While neutral and phospholipids predominate, glycolipids were also identified.

Characterization of Myelin Fractions from Human Brain White Matter

Myelin and myelin-containing (P3) fractions were prepared from human white matter by discontinuous sucrose gradient centrifugation. The myelin isolated from each of the fractions of different densities was morphologically and biochemically distinct. Light myelin fractions consisted of compact, multilamellar myelin, whereas the denser fractions consisted predominantly of loose myelin with fewer lamellae. The amounts of both basic protein and lipophilin (proteolipid protein) were reduced in the denser fractions. In contrast, the high-molecular-weight components were elevated in the dense fractions. The lipid composition was similar in all the fractions studied. Analysis of basic protein by gel electrophoresis at pH 10.6 revealed differences in basic protein microheterogeneity among the fractions. The light myelin fraction was enriched in the more positively charged basic protein components (components 1, 2, and 3), whereas these components were reduced in the denser fractions. Myelin in the dense fractions was enriched in the more modified forms of basic protein (components 6, 7, and 8). The pattern of microheterogeneity was different for basic protein isolated from myelins of a 2-year-old and an adult brain; the former showed fewer components and mainly the most cationic species. On the other hand, the pattern of microheterogeneity of basic protein isolated from the different density gradient fractions was similar for both ages.

Concomitant methylation and synthesis in vitro of Semliki Forest virus (SFV) ss RNAs by a fraction from infected cells.

Abstract The 42 S and 26 S ss SFV RNAs synthesized in vitro by the SFV RNA polymerase were also methylated in vitro by an enzyme in the mitochondrial pellet fraction, P-15, which had the activity of a guanine-7-methyltransferase. The 22 S ds RF RNA was not methylated in vitro . The methyl - 3 H radioactivity incorporated in vitro from labeled S -adenosyl- l -methionine was at the 5′-terminus of each of the ss RNAs, and none was detectable at an internal site. The 3 H-labeled cap containing oligonucleotide from the RNase T1 digest of 42 S RNA had a charge of about −6 consistent with its known m 7 GpppApUpGp sequence and that from the 26 S RNA had a charge of about −7 consistent with its known terminus of m 7 GpppApUpUpGp. The in vitro -labeled cap of both ss RNAs was m 7 GpppA. The rates of SFV RNA synthesis and methylation in vitro were linear for at least 40 min. In vitro methylation of the SFV ss RNAs absolutely depended on assay conditions which supported synthesis of ss RNAs. In contrast, transcription of 42 S and 26 S SFV RNAs in vitro was not dependent on methylation. The methylating enzyme in the P-15 fractions distributed during equilibrium centrifugation with membranous fractions of different densities in a manner similar to the distribution of the SFV RNA polymerase. It has not yet been established if this methylating activity was catalyzed by a virus-specific protein or a host protein.

The isolation and characterization of cardiac mitochondrial fractions from isoprenaline treated rats

Mitochondrial material from the ventricles of rats treated with isoprenaline 25 mg·kg −1 three times/day for 2 days was isolated either by a standard procedure using differential centrifugation or by separation of mitochondrial fractions of different densities on a discontinuous sucrose gradient. A greater percentage of mitochondrial material from isoprenaline treated myocardium was of lower density when compared to material isolated from the myocardium of saline treated controls. Characterization was carried out by relating the distribution of mitochondrial marker enzymes (succinate dehydrogenase and malate dehydrogenase) to electron microscopy data. The yield of “intact” mitochondria after isoprenaline treatment was significantly reduced ( P = 0.05), however the total amount of mitochondrial protein isolated was the same. The difference is accounted for by an increased quantity of mitochondrial fragments from isoprenaline treated hearts. The specific activity of the enzymes was reduced in mitochondria from isoprenaline treated hearts. The density gradient technique for isolating mitochondria permits the study of the effects of isoprenaline on the entire mitochondrial fraction and the more accurate definition of isoprenaline induced mitochondrial damage.