Residual electron momentum and energy in a gas ionized by a short high-power laser pulse

A study is made of the nonadiabatic dynamics of photoelectrons produced during interaction of an elliptically polarized, high-power laser pulse with a gas. Expressions for the so-called residual momentum and energy of the electrons (i.e., the mean electron momentum and energy after the passage of the pulse through the gas) are derived. The residual electron momentum and energy are investigated analytically as functions of the gas and laser parameters. A relationship is established between the residual energy and the electron temperature tensor.     

Biochemical characteristics of the Ca2+ pumping ATPase in the peribacteroid membrane from broad bean root nodules

Ca²⁺-ATPase in the peribacteroid membrane (PBM) of symbiosomes isolated from Vicia faba root nodules was characterized in terms of its hydrolytic and transport activities. Both activities were found to be pH-dependent and exhibit pH optimum at pH 7.0. Translocation of Ca²⁺ through the PBM by the Ca²⁺-ATPase was shown to be fueled by ATP and other nucleotide triphosphates in the following order: ATP?>?ITP???GTP???UTP???CTP, the K _m of the enzyme for MgATP being about 100 μM. Ca-dependent ITP-hydrolytic activity of symbiosomes was investigated in the presence of the Ca-EGTA buffer system and showed the affinity of PBM Ca²⁺-ATPase for Ca²⁺ of about 0.1 μM. The transport activity of Ca²⁺-ATPase was inhibited by erythrosin B as well as orthovanadate, but markedly stimulated by calmodulin from bovine brain. These results allowed us to conclude that this enzyme belongs to IIB-type Ca²⁺-ATPases which are present in other plant membranes.     

Ca<Superscript>2+</Superscript>-ATPase in the symbiosome membrane from broad bean root nodules: further evidence for its functioning as ATP-driven Ca<Superscript>2+</Superscript>/H<Superscript>+</Superscript> exchanger

To date, it has been established that the symbiosome membrane (SM), i.e., plant-derived membrane of symbiosomes, nitrogen-fixing compartments of legume root nodules, is equipped with Ca²⁺-ATPase transporting Ca²⁺ ions through the SM from the cytosol of infected cells into the symbiosome space (SS). Earlier in the experiments on the SM vesicles isolated from broad bean root nodules some data indicating the action of the Ca²⁺-ATPase as ATP-driven Ca²⁺/H⁺ antiporter were obtained. In the present work performed on isolated symbiosomes from the same plant object, further evidence in favor of calcium-proton countertransport mechanism of the pump operation was obtained. These were expressed in vanadate-sensitive alkalinization of the SS coupled with Ca²⁺ uptake by symbiosomes catalyzed by the SM Ca²⁺-ATPase, stimulation of the kinetics of the latter process in the response to artificial acidification of the SS and expectable modulation of ITP-hydrolyzing activity of this enzyme caused by the variation of pH within this compartment. The above findings are discussed in the framework of the model describing the mechanism of Ca²⁺-ATPase operation as an ATP-driven Ca²⁺/H⁺ exchanger and on this base allow us to put forward the hypothesis about the involvement of this enzyme in symbiosome signaling in a Ca²⁺- and pH-dependent manner.     

Bacterial production of latarcin 2a, a potent antimicrobial peptide from spider venom

Natural venoms are promising sources of candidate therapeutics including antibiotics. A recently described potent antimicrobial peptide latarcin 2a (Ltc 2a) from Lachesana tarabaevi spider venom shows a broad-spectrum antibacterial activity. This peptide consists of 26 amino acid residues and therefore its production using chemical synthesis, although trivial, is costly. We describe an easy approach to Ltc 2a production in Escherichia coli using the conventional fusion partner thioredoxin. Latarcin 2a synthetic gene was cloned into the expression vector pET-32b, which was then used to transform E. coli BL21(DE3) strain. His-tagged fusion purification was achieved using metal-chelate affinity chromatography. Since no methionine residues are present in the latarcin 2a sequence, cyanogen bromide could be effectively utilized to separate the target product from the carrier protein. Reverse-phase HPLC was used as the final step of purification; the final yield was 3 mg/L of bacterial culture. To increase the yields, we attempted incorporation of Ltc 2a tandem repeats into the fusion protein; however, production rates greatly decreased due to enhanced fusion toxicity. Moreover, we probed constructs to produce an Ltc 2a dimer and the Ltc 2a propeptide to study their functional properties. Recombinant peptides were produced at appreciable yields and biological tests to determine their activities were performed. Latarcin 2a is the first linear peptide from spider venom and one of the first membrane-active peptides from venomous animals to be biosynthetically produced.     

Differential contribution of the m7G-cap to the 5′ end-dependent translation initiation of mammalian mRNAs

Many mammalian mRNAs possess long 5′ UTRs with numerous stem-loop structures. For some of them, the presence of Internal Ribosome Entry Sites (IRESes) was suggested to explain their significant activity, especially when cap-dependent translation is compromised. To test this hypothesis, we have compared the translation initiation efficiencies of some cellular 5′ UTRs reported to have IRES-activity with those lacking IRES-elements in RNA-transfected cells and cell-free systems. Unlike viral IRESes, the tested 5′ UTRs with so-called ‘cellular IRESes’ demonstrate only background activities when placed in the intercistronic position of dicistronic RNAs. In contrast, they are very active in the monocistronic context and the cap is indispensable for their activities. Surprisingly, in cultured cells or cytoplasmic extracts both the level of stimulation with the cap and the overall translation activity do not correlate with the cumulative energy of the secondary structure of the tested 5′ UTRs. The cap positive effect is still observed under profound inhibition of translation with eIF4E-BP1 but its magnitude varies for individual 5′ UTRs irrespective of the cumulative energy of their secondary structures. Thus, it is not mandatory to invoke the IRES hypothesis, at least for some mRNAs, to explain their preferential translation when eIF4E is partially inactivated.     

Testate amoebae record from the Laptev Sea coast and its implication for the reconstruction of Late Pleistocene and Holocene environments in the Arctic Siberia

Our study aims to look for testate amobae (TA) in the surface and fossil sediments from the Cape Mamontov Klyk (73°60′–73°63′ N, 116°88′–117°18′ E), southern coast of the Laptev Sea, ca 150 km west of the Lena Delta and to discuss the potential of TA analysis for Glacial/Interglacial environmental reconstructions in Arctic Siberia. The radiocarbon age determination suggests that the studied sediments accumulated between ca 45,000 ¹⁴C yr BP and present. A total of 98 TA taxa were identified in the 10 recent surface and 59 fossil samples. Results of taxonomical identification and ecological analysis of TA in the modern and fossil samples suggest that major changes in the soil moisture conditions took place. Our results show that soil-living taxa dominated the TA assemblages at the study sites during the past 45,000 years. The environmental conditions of the study area were most favourable (relatively warm and humid) during the Kargin Interstadial (ca 45,000–25,000 ¹⁴C yr BP). An opposite situation is reconstructed for the Sartan Stadial (ca. 25,000–15,000 ¹⁴C yr BP). During the Kargin Interstadial, optimum conditions occurred between ca 44,000 and 40,000 ¹⁴C yr BP characterised by highest TA abundances and taxa diversity. This initial optimal phase was followed by the interval with drier and colder conditions about 40,000–30,000 ¹⁴C yr BP. The sediments dated between ca. 24,000 and 18,000 ¹⁴C yr BP show low TA abundances and diversity, in agreement with the much colder and drier environments during the maximum phase of the Last Glacial. The onset of the Holocene is indicated by a broad representation of obligate hydrophilic taxa, especially from genus Difflugia, suggesting wet and relatively warm conditions. By comparison with other environmental proxies used in the studied sections as well as from the neighbouring arctic regions our results suggest that TA analysis can provide valuable information, contributing to the better understanding of the Late Quaternary climate and environments in Arctic Siberia.     

New polypeptide components from the <Emphasis Type="Italic">Heteractis crispa</Emphasis> sea anemone with analgesic activity

Two new polypeptide components which exhibited an analgesic effect in experiments on mice were isolated from the Heteractis crispa sea tropical anemone by the combination of chromatographic methods. The APHC2 and APHC3 new polypeptides consisted of 56 amino acid residues and contained six cysteine residues. Their complete amino acid sequence was determined by the methods of Edman sequencing, mass spectrometry, and peptide mapping. An analysis of the primary structure of the new peptides allowed for their attribution to a large group of trypsin inhibitors of the Kunitz type. An interesting biological function of the new polypeptides was their analgesic effect on mammals, which is possibly realized via the modulation of the activity of the TRPV1 receptor and was not associated with the residual inhibiting activity towards trypsin and chymotrypsin. The analgesic activity of the APHC3 polypeptide was measured on the hot plate model of acute pain and was significantly higher than that of APHC2. Methods of preparation of the recombinant analogues were created for both polypeptides.     

Tuning a polar molecule for selective cytoplasmic delivery by a pH (Low) insertion peptide

Drug molecules are typically hydrophobic and small in order to traverse membranes to reach cytoplasmic targets, but we have discovered that more polar molecules can be delivered across membranes using water-soluble, moderately hydrophobic membrane peptides of the pHLIP (pH low insertion peptide) family. Delivery of polar cargo molecules could expand the chemical landscape for pharmacological agents that have useful activity but are too polar by normal drug criteria. The spontaneous insertion and folding of the pHLIP peptide across a lipid bilayer seeks a free energy minimum, and insertion is accompanied by a release of energy that can be used to translocate cell-impermeable cargo molecules. In this study, we report our first attempt to tune the hydrophobicity of a polar cargo, phallacidin, in a systematic manner. We present the design, synthesis, and characterization of three phallacidin cargoes, where the hydrophobicity of the cargo was tuned by the attachment of diamines of various lengths of hydrophobic chains. The phallacidin cargoes were conjugated to pHLIP and shown to selectively inhibit the proliferation of cancer cells in a concentration-dependent manner at low pH.     

Late Quaternary paleoenvironmental records from the western Lena Delta,Arctic Siberia

The three main Lena Delta terraces were formed during different stages of the late Quaternary. While only the first floodplain terrace is connected with active deltaic processes, the second and third terraces, which dominate the western part of the delta, are erosional remnants of arctic paleolandscapes affected by periglacial processes. The landscape dynamics of the second and the third terraces, and their relationship to each other, are of particular importance in any effort to elucidate the late Quaternary paleoenvironment of western Beringia.Multidisciplinary studies of permafrost deposits on the second terrace were carried out at several sites of the Arga Complex, named after the largest delta island, Arga–Muora–Sise. The frozen sediments predominantly consist of fluvial sands several tens of meters thick, radiocarbon-dated from > 52 to 16 kyr BP. These sands were deposited under changing fluvial conditions in a dynamic system of shifting river channels, and have been additionally modified by synsedimentary and postsedimentary cryogenesis. Later thermokarst processes affected this late Pleistocene fluvial landscape during the Lateglacial and the Holocene. In addition, eolian activity reworked the fluvial sands on exposed surfaces at least since the Lateglacial, resulting in dune formation in some areas. Contrary to the Arga Complex, the third terrace is mainly composed of polygenetic alluvial and proluvial ice-rich permafrost sequences (Ice Complex deposits) radiocarbon-dated from 50 to 17 kyr BP which cover older fluvial sand units luminescence-dated to about 100–50 kyr BP. Paleoecological records reflect tundra-steppe conditions that varied locally, depending on landscape dynamics, during the Marine Isotope Stage (MIS) 4 and 3 periods, and a persistent change to shrub and arctic tundra during Lateglacial and Holocene periods.The study results indicate a continuous fluvial sedimentation environment for the Laptev Sea shelf in the region of the second Lena Delta terrace during the late Pleistocene, and confirm the presence of a dynamic channel system of the paleo-Lena River that flowed at the same time as the nearby subaerial Ice Complex deposits were being formed.