Possible Mechanism For Generation Research Articles

439 Melanoma cells export functional proteasomes by way of microvesiculation: a possible mechanism for generation of plasmatic proteasomes

Plasmatic proteasomes (p-proteasomes) are a reliable marker for metastatic dissemination in melanoma patients. Recent works have suggested that p-proteasome partially originated from tumour cell secretion via exosomes, which are also considered as a new biomarker for metastatic melanoma. Our objectives were to investigate the origin, mechanism of secretion and functionality of the melanoma p-proteasomes. We show by proteasome purification either from culture supernatant of melanoma cell lines (A-375, SK-MEL-28) or from plasma of melanoma patients, that the extracellular proteasome is released essentially as an assembled 20S core particle, contrarily to proteasome analyzed from cell lysate, which presents additional 26S capped proteasome. Using specific fluorogenic substrates we demonstrate that these extracellular proteasomes are functional and possess all the peptidase activities associated with b1, b2 and b5 subunits. There is no correlation between exosome and proteasome concentrations determined by ELISA in the plasma of melanoma patients. Immunoisolation of secreted proteasome using a7 antibody adsorbed on magnetic beads and pull-down experiments show that secreted proteasomes are not enwrapped in exosomes. To our point of view, previous reports of 20S proteasome subunits in exosomes are rather due to a co-purification along the exosome preparation. Extracellular proteasome concentration is increased in the secretome of melanoma cell lines after stimulation of membrane blebbing with the ionophore A23187. Moreover, proteasome is associated with microvesicles as shown by gel filtration experiments and immobilization of microvesicles on lectin-sepharose. Altogether our results show that melanoma cells secrete functional 20S proteasomes at least in part by membrane blebbing and microvesiculation and not through exosomal pathway.

Transport of melt and volatiles in magmas inferred from kinetic experiments on the partial melting of granitic rocks

Partial melting of crustal rocks is responsible for the formation of silicic magmas and crustal differentiation. Determining the mechanisms and effects of partial melting is necessary to understand the geochemical signature of the magmas and the transport of melt and volatiles in the crust. To this end, we have experimentally reproduced the partial melting of granitic rock under three different conditions: i) partial melting in a closed system (dry and hydrous conditions); ii) partial melting in the presence of a discontinuity, represented by a channel of synthetic haplogranite and iii) assimilation of granitic rock by a hydrous trachyandesitic melt. Experiments were performed at temperatures between 750 and 1000 °C and pressures between 300 and 500 MPa, with durations ranging from 24 to 240 h. Partial melting initiates at temperatures higher than 750 °C as a result of both dehydration melting of hydrous minerals and melting at grain boundaries. The interplay between the two mechanisms determines the complex evolution of melt composition at the various degrees of partial melting. Core-to-rim compositional profiles of residual feldspars in contact with the melt attest to a rapid mineral-melt re-equilibration (240 h). When a melt channel intersects the granite, the melt produced at the grain boundaries is rapidly segregated within the channel and mineral-melt exchange reactions are inhibited. In turn, the melt in the channel is enriched in H2O and incompatible trace elements. When in contact with a hydrous, partially molten trachyandesite, complete dissolution of the granite occurs at 900 °C, assisted by the migration of H2O from the crystallizing trachyandesitic melt. The melting-assimilation process results in a system characterized by a crystalline trachyandesite enclosing a hybrid trachytic melt, produced by the chemical mixing of the granitic melt with the melt segregated from the crystalline trachyandesite.Our experimental results indicate that partial melting could be extremely common in granitic bodies and yield no traces in the residual rock after segregation of the interstitial melt. In contrast, core-to-rim profiles of feldspars may preserve a record of the interaction between residual minerals and the extracted melt. Fast segregation of melts enriched in volatiles and incompatible trace elements, produced by breakdown of hydrous minerals, may represent a possible mechanism for generation of pegmatites.

Detection of reactive oxygen species (ROS) and investigation of efficient visible-light-responsive photocatalysis via nanoscale PbSe sensitized TiO2

In this study, a novel visible-light-responsive PbSe–TiO2 nanocomposite photocatalysts were successfully synthesized through a facile sonochemical-assisted method, and characterized by XRD, SEM–EDX, TEM, and DRS to confirm its structure, morphology, composition, and optical property. In decolorization of rhodamine B, a significant enhancement in the reaction rate was observed with PbSe–TiO2 composite, compared to the pure TiO2. The generation of reactive oxygen species was detected through the oxidation reaction from 1,5-diphenyl carbazide (DPCI) to 1,5-diphenyl carbazone (DPCO). The high photocatalytic activity can be attributed to the synergetic effect of PbSe nanoparticles and TiO2 by extending the spectral response of TiO2 to visible region and also help to reduce the charge recombination. Finally, the possible mechanism for generation of reactive oxygen species under visible light irradiation was proposed as well.

Origin and evolution of granitoids associated with the Kadiri greenstone belt, eastern Dharwar craton: A history of orogenic to anorogenic magmatism

Different tectonic models have been proposed to explain the Neoarchaean evolution of the eastern Dharwar craton (EDC). Here we present whole-rock elemental and Nd isotopic compositions coupled with zircon U–Pb age and trace elemental data on granitoids associated with the Neoarchaean Kadiri greenstone belt, EDC to track the tectonic evolutionary history of the terrain. Earlier works on volcanic rocks of the Kadiri belt (tholeiitic oceanic plateau basalt, high Mg# andesite and potassic adakite) envisaged continental margin arc–oceanic plateau collision. In this work the oldest recognized granitoid is a 2.56Ga syntectonic, sanukitoid-like hornblende granodiorite enriched in large-ion lithophile as well as ferromagnesian elements. It was probably derived from a metasomatized mantle wedge above a subduction zone. This is followed by syntectonic emplacement of 2.54Ga transitional TTGs and potassic adakitic volcanic rocks. Intrusion of 2.51–2.52Ga crustally derived granites (mostly K-rich; ɛNd=+0.9 to −3.7) marks the end of orogenesis in the area. A convergent orogenic setting characterized by assembly of diverse terranes, repeated slab-break-off and crustal reworking is proposed to interpret the association of various granitoids and volcanic rocks. Finally, intrusion of crustally derived, highly silicic, K-rich A-type granite (ɛNd=−0.6 to −4.8) and mantle-derived syenite occurred in a post-subduction, non-compressive environment during Palaeoproterozoic. Lithospheric delamination and attendant mantle melting and crustal reworking are suggested as possible mechanism for generation of these rocks. The negative ɛNd values and Mesoarchaean Nd depleted mantle model ages of some Neoarchaean to Palaeoproterozoic Kadiri granitoids attest to the presence of older crust in the eastern part of the EDC. The final cratonization of the EDC (2.52–2.50Ga) occurred later than in most of the other cratons.

Spiral motion formation in astrophysics

Motion of charged matter in gravitational and large-scale magnetic fields represents one of the most discussed topics in astrophysics. Here, one of the particular problems is addressed: the spiral motion of charged test particles as a possible mechanism for generation of weak toroidal magnetic field (magnetic loop) complementary to the prescribed large-scale one. To this aim, by contrast with the usually assumed scenario with particles circling in spirals along with the magnetic lines of a magnetic field dominating over gravity, the perturbed stable circular equatorial motion is discussed when the gravity of the central object plays at least a comparable role to electromagnetism. It is shown that the proper relation between the epicyclic and orbital frequencies necessary for the spiral motion cannot be easily achieved in the basic fields configuration within the Newtonian theory. The inclusion of the strong-field general relativistic effect, however, yields the desired conditions for particles to orbit in spirals.

T lymphocytes export proteasomes by way of microparticles: a possible mechanism for generation of extracellular proteasomes

The 20S proteasome is almost exclusively localized within cells. High levels of extracellular proteasomes are also found circulating in the blood plasma of patients suffering from a variety of inflammatory, autoimmune and neoplastic diseases. However, the origin of these proteasomes remained enigmatic. Since the proteome of microparticles, small membrane enclosed vesicles released from cells, was shown to contain proteasomal subunits, we studied whether intact proteasomes are actively released into the extracellular space. Using human primary T lymphocytes stimulated with CaCl2 and the calcium ionophore A23187 to induce membrane blebbing we demonstrate that microparticles contain proteolytically active 20S proteasomes as well as the proteasome activator PA28 and subunits of the 19S proteasome regulator. Furthermore, our experiments reveal that incubation of in vitro generated T lymphocyte-microparticles with sphingomyelinase results in the hydrolysis of the microparticle membranes and subsequent release of proteasomes from the vesicles. Thus, we here show for the first time that functional proteasomes can be exported from activated immune cells by way of microparticles, the dissolution of which may finally lead to the generation of extracellular proteasomes.

Dissipative instabilities in a mesospheric plasma with the aerosol charging processes taken into account

We consider dissipative instabilities of a flow of large aerosol particles as a possible mechanism for generation of electric-field and charged-particle density irregularities in the middle atmosphere. A dispersion equation describing the properties of the spectral component of a quasistatic electric field with allowance for the aerosol charging inertia and external stationary electric field is obtained. The equation is used to study characteristics of two possible instabilities, namely, the instability of a dust-acoustic mode and the instability of an additional low-frequency mode stimulated by the charging inertia. Dependences of the growth rates of both instabilities on the parameters of the medium and the external stationary electric field are obtained. Quantitative estimates for the parameters of the aerosol, ion, and electron components and external factors that are necessary for the excitation of instabilities in the region of the existence of summer polar mesospheric echo, as well as those for spatial scales of unstable perturbations, are given.

Thermospheric dark band structures at low latitudes in the Southern Hemisphere under different solar activity conditions: A study using OI 630 nm emission all‐sky images

Using ground‐based measurements we investigate the occurrence of dark band structures in the OI 630 nm nightglow emission all‐sky images in the Brazilian low latitude region during the periods from January 1990 to December 1990 (high solar activity period‐HSA), May 1995 to July 1996 (low solar activity period‐LSA) and from January 1997 to December 1999 (ascending solar activity period‐ASA). Unfortunately we do not have all‐sky images for the descending phase of solar activity period. The OI 630 nm images obtained during these periods show thermospheric Dark Band Structures (DBS) in the low latitudes region propagating from southeast to northwest. These dark patches moved with average speed of about 50–200 m/s at an altitude of 220–300 km, which is the typical altitude range of the OI 630.0 nm airglow emission. Only during low solar activity period (LSA) and ascending solar activity period (ASA), the DBS occurrences were observed in the OI 630 nm nightglow emission all‐sky images. It should be pointed out that these thermospheric/ionospheric events are not related to geomagnetic disturbed conditions. In this paper, we present and discuss this phenomena in the Brazilian sector under different solar activity conditions. A possible mechanism for generation of these dark band structures is presented.

Thermospheric dark band structures observed in all‐sky OI 630 nm emission images over the Brazilian low‐latitude sector

Using two ground‐based all‐sky imaging systems, measurements of moving dark band structures in the OI 630.0 nm nightglow emission were detected in the low‐latitude region of Brazil. On the nights of 30–31 August 1995, 18–19 July 1998, and 13–14 July 1999, the all‐sky imaging observations of the OI 630 nm emission, carried out at Cachoeira Paulista (22.7°S, 45°W, magnetic declination 20°W), Brazil, showed dark band structures that stretched across the entire image and propagated from southeast to northwest. The observed band structures are thus most likely formed in the midlatitude region and move into the field of view. Digisonde observations, available for two of the events, registered abrupt increases in both the F‐layer peak height (hmF2) and minimum virtual height (h'F) on 19 July 1998 and 13 July 1999, when the low‐intensity band passed over Cachoeira Paulista. It should be pointed out that these thermospheric events are not related to geomagnetic disturbed conditions, as the nights for which data are presented are geomagnetically quiet (Kp < 2). In this paper we present and discuss the first observations of these thermospheric dark band structures in the Brazilian sector and their effects on the nighttime ionosphere. A possible mechanism for generation of these dark band structures is presented.

Insights into the Mechanism of BN Generation via Boron Triazide Precursor: Theoretical Study

Potential-energy surfaces for unimolecular decomposition of B(N3)(3) have been studied to understand the possible mechanism for BN generation. The decomposition of B(N3)(3) takes place on either the singlet and triplet surface, and both processes are high exothermic and obey sequential mechanisms. For the singlet reaction, the rate-determining step corresponds to cleavage of the first azide bond and linear (1)NBNN instead of (1)BN was suggested as the dominant product at room temperature. For the triplet surface, a fragment process from (3)BN(7) to (3)BN(5) is predicted to be the rate-determining step; once this barrier is counteracted, the subsequent decomposition processes could easily occur to form final product (3)BN. In addition, the possible mechanism for generating BN film via B(N3)(3) was discussed based on MC-SCF calculation results. These findings might be helpful in understanding the controllable decomposition of B(N3)(3) as well as its application in generating BN films.

MV Lyrae: Photometric study at high state

Photoelectric observations of novalike MV Lyr in a standard UBV system were carried out at Rozhen and Belogradchik observatories in 1992 and 1993. During all the nights of observations the star was in high state (V 12.5 mag). The observing runs performed in U and B bands show strong flickering activity and a typical shape of the red noise power spectrum. The periodogram anal- ysis of time series shows quasi-periodic oscillations with a period of about 50 min. The excitation of trapped oscilla- tions at the outer edge of the accretion disc, has been pro- posed as a possible mechanism for generation of MV Lyr quasi-periodic oscillations. The properties of the flickering in MV Lyr light curves were determined.

Instability of plasma vibrations in a wide parabolic GaAs/AlGaAs quantum well caused by plasmon-assisted tunnelling. A possible mechanism for generation and amplification of far-infrared radiation

We consider a wide parabolic GaAs/AlGaAs quantum well placed between two metal plates so that direct current can flow across the well. Sloshing plasma oscillations of the charge stored in the well modulate the direct current and charges on the plates and in the well acquire an alternating component. The system can be considered as a capacitor with one plate, the electronic slab in the well, performing mechanical oscillations (plasmons). The electrostatic forces acting between the plates of this capacitor cause the oscillations to build up. We derive an expression for the threshold and estimate the power of the infrared radiation which can be delivered by the structure.

Numerical simulations of topographic Rossby waves along the East Greenland Front

Topographic Rossby waves propagating along the East Greenland Front between 77° and 72°N are simulated using a primitive‐equation ocean model of the Greenland Sea. The waves are prominent in both barotropic and baroclinic experiments, and their estimated wave period and wavelength are about 17.3 hours and 363 km, respectively. A possible mechanism for generation of topographic Rossby waves is presented. The dominant along‐slope component of the group velocity implies that the bulk of the energy propagates along the shelf slope of Greenland toward the northeast. Existence of the offshore component indicates that some energy is available for cross‐frontal mixing within the East Greenland Front.

Optical activity of hemoproteins in the Soret region. Circular dichroism of the heme undecapeptide of cytochrome c in aqueous solution.

Different possible mechanism for generation of optical activity of hemoproteins in the Soret region are reconsidered. The heme undecapeptide of cytochrome c does not contain aromatic amino acid residues, so its considerable optical activity cannot be due to coupling of heme pi pi * transitions with those of aromatic residues. CD data for the heme undecapeptide and for ferrimyoglobin and some of their complexes with small molecules are presented and critically compared. Symmetrically coordinated imidazole complexes show rotational strengths of the same magnitude as those of corresponding nonsymmetrically coordinated compounds. Inherent chirality in the bound heme is inferred to be a significant source of optical activity in the heme undecapeptide. Theoretical calculations based upon a molecular dynamics simulation support this proposal. Coupled oscillator interactions with the peptide pi pi * transitions and with the high-energy transitions in the peptide groups and thioether sulfurs, as modeled by polarizabilities, also make significant contributions. These same mechanisms must also be considered in hemoproteins in general.

Several short interspersed repetitive elements (SINEs) in distant species may have originated from a common ancestral retrovirus: characterization of a squid SINE and a possible mechanism for generation of tRNA-derived retroposons.

Using labeled transcripts generated in vitro from squid total genomic DNA as a probe, we isolated and characterized a SINE that is present in the squid genome. The squid SINE appears to be derived from a tRNA(Lys). When the consensus sequences of five different SINEs with a tRNA(Lys)-like structure from distantly related species, including squid, were aligned, we found in the tRNA-unrelated region two sequence motifs that were almost identical among these five SINEs. This observation suggests a common evolutionary origin for these SINEs and/or some function(s) for these motifs. Similar sequences were unexpectedly found to be present in sequences complementary to the U5 regions of several mammalian retroviruses whose primer is a tRNA(Lys). On the basis of these findings, we present a model for the generation of SINEs. We propose that they are derived from a "strong-stop DNA" with a primer tRNA(Lys) that is an intermediate in the reverse transcription of certain retroviruses. Our model suggests that a certain group of SINEs may have been generated by horizontal transmission, although it is not clear whether information was transmitted via a similar retrovirus or via an RNA or DNA of a SINE.

Oxidation as a possible mechanism of cellular aging: vitamin E deficiency causes premature aging and IgG binding to erythrocytes.

Senescent-cell antigen is a "neo-antigen" that appears on the surface of senescent cells and initiates IgG binding and cellular removal. As an approach to evaluating oxidation as a possible mechanism for generation of senescent-cell antigen, we studied erythrocytes from vitamin E-deficient rats. Vitamin E is localized primarily in cellular membranes. Its major role is the termination of free-radical chain reactions propagated by the polyunsaturated fatty acids of membrane propagated by the polyunsaturated fatty acids of membrane phospholipids. Results of our studies indicate that erythrocytes of all ages from vitamin E-deficient rats behave like old erythrocytes from normal rats, as determined by their susceptibility to phagocytosis, IgG binding, anion transport ability, and glyceraldehyde-3-phosphate dehydrogenase activity. Increased breakdown products of band 3 were observed with immunoblotting in membranes of erythrocytes from vitamin E-deficient rats. Breakdown products of band 3 are known to increase as cells age in normal individuals. The data suggest that oxidation may be a possible mechanism for erythrocyte aging and generation of senescent-cell antigen in vivo.

Partially coherent radiation by charged particle beams in the ionosphere

Coherent effects in the radiation from finite-sized nonuniform particle beams penetrating the ionosphere are studied. For illustrative purposes, special beam structures are assumed which permit the coherent radiation effects to be extracted from the complicated integrals of the more general theory as an explicit analytic factor. The results are used to show a possible mechanism for generation of narrow-band low-frequency noise peaks.

Rapid Geomagnetic Fluctuations

The article presents an investigation of VLF-oscillations (0.2–200 c/s) in the earth's magnetic field. The measurements were made in the archipelago of Stockholm (59° N) during the period July 1957—June 1959. The oscillations were recorded by two different instruments: a high-speed Heiland oscillograph and a low-speed Esterline-Angus recorder. In the Esterline-Angus diagrams a morning minimum at about 8 o'clock local time was found. In the Heiland oscillograms three different features were found: 1. Frequent occurrence of sinusoidal fluctuations presenting a few very narrow bands; 2. Oscillations in the H- and Z-component are sometimes simultaneous, sometimes not; 3. The amplitudes in the Z-component are smaller than in the H-component. It has not been possible to find a correlation between the fluctuations investigated here and other geophysical phenomena. A possible mechanism for generation of the sinusoidal oscillations is discussed. DOI: 10.1111/j.2153-3490.1961.tb00105.x

Rapid Geomagnetic Fluctuations

The article presents an investigation of VLF-oscillations (0.2—200 c/s) in the earth’s magnetic field. The measurements were made in the archipelago of Stockholm (59’ N) during the period July 1957—June 1959. The oscillations were recorded by two different instruments : a high-speed Heiland oscillograph and a low-speed Esterline-Angus recorder. In the Esterline-Angus diagrams a morning minimum at about 8 o’clock local time was found. In the Heiland oscillograms three different features were found: 1. Frequent occurrence of sinusoidal fluctuations presenting a few very narrow bands; 2. Oscillations in the H- and Z-component are sometimes simultaneous, sometimes not ; 3. The amplitudes in the Z-component are smaller than in the H-component. It has not been possible to find a correlation between the fluctuations investigated here and other geophysical phenomena. A possible mechanism for generation of the sinusoidal oscillations is discussed.