bluuebunny/crossref_metadata_2025 huggingface dataset:
Amelioration of global warming by controlled enhancement of the albedo and longevity of low‐level maritime clouds
Authors: Latham John
Published: April 2003

A technique is proposed for controlled enhancement of droplet concentrations in low‐level maritime clouds, with corresponding increase in their albedo and longevity, thereby producing a cooling effect. It involves dissemination at the ocean surface of small seawater droplets which act as cloud condensation nuclei (CCN). It has low ecological impact. Copyright © 2002 Royal Meteorological Society.
Late Holocene Paleoclimatic Changes in Western Central Africa Inferred from Mineral Abundance in Dated Sediments from Lake Ossa (Southwest Cameroon)
Authors: Wirrmann Denis , Bertaux Jacques , Kossoni Alice
Published: April 2003

Minerals derived from catchment soils were determined using FTIR spectroscopy in the well-dated core OW4 from Lake Ossa, a lowland rainforest area in Cameroon. This quantification provides a hydrologic record indicating that the magnitude of runoff events, and by inference, rainfall pattern, has varied during the Late Holocene. The comparison between minerogenic inputs and vegetation changes improves the understanding of the inferred climate dynamics. Since at least 5400 cal yr B.P., the paleomonsoon rainfall intensity decreased, as shown by a general decrease in mineral fluxes. This observation is consistent with a gradual weakening of the boreal summer insolation in tropical latitudes. However, the major vegetational change lags behind the onset of the decrease in mineral fluxes. From 2800 to ca 1000 cal yr B.P., the forest receded: the amount of rainforest taxa decreased and is replaced by pioneer trees and Poaceae, when the mineral fluxes attained their lowest values. This episode of maximum dryness is attributed to an abrupt climatic event of global significance which is superimposed onto the paleomonsoon variability. It is related to a cold event, which in turn produced a change in the lower atmospheric circulation that was characterized by a strengthening of northern trade winds, probably correlated with sea-surface temperature variations in the eastern tropical Atlantic area.
Holocene Vegetation History from Fossil Rodent Middens near Arequipa, Peru
Authors: Holmgren Camille A. , Betancourt Julio L. , Rylander Kate Aasen , Roque Jose , Tovar Oscar , Zeballos Horacio , Linares Eliana , Quade Jay
Published: April 2003

Rodent (Abrocoma, Lagidium, Phyllotis) middens collected from 2350 to 2750 m elevation near Arequipa, Peru (16°S), provide an ∼9600-yr vegetation history of the northern Atacama Desert, based on identification of >50 species of plant macrofossils. These midden floras show considerable stability throughout the Holocene, with slightly more mesophytic plant assemblages in the middle Holocene. Unlike the southwestern United States, rodent middens of mid-Holocene age are common. In the Arequipa area, the midden record does not reflect any effects of a mid-Holocene mega drought proposed from the extreme lowstand (100 m below modern levels, >6000 to 3500 yr B.P.) of Lake Titicaca, only 200 km east of Arequipa. This is perhaps not surprising, given other evidence for wetter summers on the Pacific slope of the Andes during the middle Holocene as well as the poor correlation of summer rainfall among modern weather stations in the central Andes-Atacama Desert. The apparent difference in paleoclimatic reconstructions suggests that it is premature to relate changes observed during the Holocene to changes in El Niño Southern Oscillation modes.
Long Plio-Pleistocene Terrestrial Record of Climate Change and Mammal Turnover in Southern Spain
Authors: Agustı́ Jordi , Oms Oriol , Remacha Eduard
Published: April 2003

Cyclostratigraphic analysis of the Pliocene Zújar section (Guadix-Baza Basin, southeastern Spain) has enabled the recognition of a number of climatically forced cycles reflecting alternating dry and wet periods. Peaks of aridity are recorded at ca. 3.95, 3.55, 3.2, 2.8, and 1.8 myr B.P. The first dry period at about 4.0 myr B.P. corresponds to the early Ruscinian Mammal age, while the second arid interval at about 3.6 myr B.P. corresponds to the establishment of the Mediterranean double seasonality. The significant mammal turnover between the late Ruscinian and early Villanyian stages is placed between chron 2An.2n and the very base of chron 2An.1n, coincident with the dry phase recognized at about 3.2 myr B.P. The fourth aridity maximum at 2.8 myr B.P. roughly coincides with the Equus event in western Europe and is probably related to the beginning of the glacial–interglacial dynamics in the Northern Hemisphere. Finally, the last dry peak at about 1.8 myr B.P. is probably related to the set of mammalian events characterizing the transition from the late Pliocene faunas to those of the early Pleistocene.
Late Quaternary Water-Level Variations and Vegetation History at Crooked Pond, Southeastern Massachusetts
Authors: Shuman Bryan , Bravo Jennifer , Kaye Jonathan , Lynch Jason A. , Newby Paige , Webb Thompson
Published: April 2003

Sediment cores collected along a transect in Crooked Pond, southeastern Massachusetts, provide evidence of water-level changes between 15,000 cal yr B.P. and present. The extent of fine-grained, detrital, organic accumulation in the basin, inferred from sediment and pollen stratigraphies, varied over time and indicates low water levels between 11,200 and 8000 cal yr B.P. and from ca. 5300 to 3200 cal yr B.P. This history is consistent with the paleohydrology records from nearby Makepeace Cedar Swamp and other sites from New England and eastern Canada and with temporal patterns of regional changes in effective soil moisture inferred from pollen data. The similarities among these records indicate that (1) regional conditions were drier than today when white pine (Pinus strobus) grew abundantly in southern New England (11,200 to 9500 cal yr B.P.); (2) higher moisture levels existed between 8000 and 5500 cal yr B.P., possibly caused by increased meridonal circulation as the influence of the Laurentide ice sheet waned; and (3) drier conditions possibly contributed to the regional decline in hemlock (Tsuga) abundances at 5300 cal yr B.P. Although sea-level rise may have been an influence, moist climatic conditions during the late Holocene were the primary reason for a dramatic rise in water-table elevations.
Dating Early and Middle (Reid) Pleistocene Glaciations in Central Yukon by Tephrochronology
Authors: Westgate John A. , Preece Shari J. , Froese Duane G. , Walter Robert C. , Sandhu Amanjit S. , Schweger Charles E.
Published: April 2003

The late Cenozoic deposits of central Yukon contain numerous distal tephra beds, derived from vents in the Wrangell Mountains and Aleutian arc–Alaska Peninsula region. We use a few of these tephra beds to gain a better understanding on the timing of extensive Pleistocene glaciations that affected this area. Exposures at Fort Selkirk show that the Cordilleran Ice Sheet advanced close to the outer limit of glaciation about 1.5 myr ago. At the Midnight Dome Terrace, near Dawson City, exposed outwash gravel, aeolian sand, and loess, related to valley glaciers in the adjacent Ogilvie Mountains, are of the same age. Reid glacial deposits at Ash Bend on the Stewart River are older than oxygen isotope stage (OIS) 6 and likely of OIS 8 age, that is, about 250,000 yr B.P. Supporting evidence for this chronology comes from major peaks in the rates of terrigeneous sediment input into the Gulf of Alaska at 1.5 and 0.25 myr B.P.
Holocene Soil Development on Till and Outwash Inferred from Lake-Sediment Geochemistry in Michigan and Wisconsin
Authors: Ewing Holly A. , Nater Edward A.
Published: April 2003

Two geochemical techniques from soil mineralogy were used with lake sediment to reconstruct soil development in the catchments of two lakes—one on outwash and the other on till—in the Great Lakes region. A sodium pyrophosphate extraction provides information about leaching of exchangeable and organically complexed cations from terrestrial sources, while an acidified ammonium oxalate extraction removes mineral materials without well-developed crystalline structure that are indicative of podzolization. More evidence of pedogenesis is preserved in sediment of the lake on outwash—likely a result of greater retention of material within the soil profile in the catchment on till. This difference between the records suggests that excessively well-drained (leaky) catchments may provide better records of soil development than those with higher water-holding capacity. Evidence of acidification and podzolization appeared first at the lake on till and 4500 years later at the lake on outwash. Both records reveal a late Holocene intensification of weathering that coincided with a regional climatic change to greater moisture availability. The variability in weathering rates observed presents a more complex picture of weathering than the simple exponential functions often assumed in chronosequence studies. Use of lake sediment records provides better temporal resolution of significant events in soil formation than could be achieved using a chronosequence approach.
Timing and Extent of Allerød and Younger Dryas Age (ca. 12,500–10,00014C yr B.P.) Oscillations of the Cordilleran Ice Sheet in the Fraser Lowland, Western North America
Authors: Kovanen Dori J. , Easterbrook Don J.
Published: April 2003

The use of shaded digital topographic models to visualizes suites of topographic features, stratigraphy, and field mapping reveals newly recognized multiple moraines associated with oscillations of the remnants of the Cordilleran Ice Sheet in the Fraser Lowland along the western Washington–British Columbia border. Morphologic features show the extent of ice represented by Sumas Drift (ca. 11,600–10,00014C yr B.P.), following ca. 3000 yr of retreat from the glacial maximum (Fraser Glaciation) positions 80 km south of Seattle and in the Strait of Juan de Fuca. The paleogeography of the ice margin and timing of ice retreat during the Sumas Stade is reconstructed and bracketed by 70 radiocarbon dates (24 on marine shells, 46 on wood and peat), which are secured by morphologic and stratigraphic evidence. Four topographically distinct phases of the Sumas deglaciation model are suggested.

Phase SI: 11,600–<11,40014C yr B.P., outermost drift, scattered remnants of ice-contact deposits

Phase SII: 11,600–11,40014C yr B.P., glacier readvance, building prominent moraine followed by glacier retreat

Phase SIII: 10,980–10,25014C yr B.P., glacier readvance building of multiple moraines followed by glacier retreat

Phase SIV: >10,250–10,000?14C yr B.P., glacier readvance, building of inner moraine followed by glacier retreat
Holocene Lake-Effect Precipitation in Northern Michigan
Authors: Delcourt Paul A. , Nester Peter L. , Delcourt Hazel R. , Mora Claudia I. , Orvis Kenneth H.
Published: April 2003

Holocene sediments from Nelson Lake, on Michigan's eastern Upper Peninsula, provide isotopic, pollen, and charcoal evidence for a two-step sequence of changes in moisture source and increased lake-effect precipitation during the late Holocene. Between 8000 and 5300 cal yr B.P., a warm, dry climate and zonal atmospheric circulation produced enriched stable oxygen and carbon isotopic values in combination with high percentages of pine pollen and sustained influx of charcoal particles. After 5300 cal yr B.P., decreasing isotopic values in marl and increasing pollen percentages of mesic hardwoods and northern white cedar indicate increased meridional air flow and precipitation from cold winter storms generated in Alberta, Canada. After 3000 cal yr B.P., abrupt declines in values of δ13C and δ18O and increased pollen representation of hemlock, American beech, spruce, and aquatic plants indicate paludification from increased lake-effect snowfall. The moisture was derived from the Great Lakes and transported by Alberta cyclonic storms that were steered across Lakes Superior and Michigan by a southward shift in the modal winter position of the polar jet stream.
Abnormally phosphorylated tau in SY5Y human neuroblastoma cells
Authors: Tanaka Toshihisa , Iqbal Khalid , Trenkner Ekkhart , Dong Jie Liu  , Grundke-Iqbal Inge
Published: April 2003

In Alzheimer disease (AD) the microtubule associated protein (MAP) tau is hyperphosphorylated at several sites. In the present study, like AD tau, tau in the human neuroblastoma SH‐SY5Y was found to be hyperphosphorylated, at Ser‐199/202, Thr‐231, Ser‐396 and Ser‐404. However, in contrast to AD, the tau in SY5Y cells was not hyperphosphorylated at Ser‐235 and there was only one tau isoform. Quantitative analysis revealed that approximately 80% of the SY5Y‐ tau was phosphorylated at Ser‐199/202. The phosphorylated tau was deposited in perikarya and processes of the cells whereas most of the unphosphorylated (at Ser‐199/202) tau was localized in the nucleus. Tau from the cell lysates did not bind to taxol‐stabilized microtubules. In contrast, MAP1b and MAP2 from cell lysates bound to stabilized microtubules in vitro and were associated to the microtubule network in situ. Phosphorylation of tau at high levels, its inactivity with microtubules and its accumulation in SY5Y cells provide for the first time a cell model of cytoskeletal changes seen in AD.
Multiple isoforms of Pisum trypsin inhibitors result from modification of two primary gene products
Authors: Domoney C. , Welham T. , Sidebottom C. , Firmin J.L.
Published: April 2003

Characterization of Pisum (pea) seed trypsin inhibitors (TI) and their corresponding cDNAs indicates that the pea TI gene family contains two genes. The existence of multiple TI isoforms can be attributed to post‐translational modifications of primary gene products. Post‐translational processing at the C‐terminus during the desiccation stage of seed development results in the appearance of TI isoforms with increased affinity for the target enzyme, trypsin.
Cell surface binding of TIMP‐2 and pro‐MMP‐2/TIMP‐2 complex
Authors: Emmert-Buck Michael R. , Emonard HervéP. , Corcoran Marta L. , Krutzsch Henry C. , Foidart Jean-Michel , Stetler-Stevenson William G.
Published: April 2003

Tissue inhibitor of metalloproteinases (TIMP‐2) is a low molecular weight proteinase inhibitor capable of inhibiting activated matrix metalloproteinases (MMPs). TIMP‐2 is found both free and in a 1:1 stoichiometric complex with the pro‐enzyme form of MMP‐2 (pro‐MMP‐2/TIMP‐2 complex). We have measured the binding of recombinant TIMP‐2 to intact HT‐1080 and MCF‐7 cells. HT‐1080 cells in suspension bound 125I‐labeled rTIMP‐2 with a K
d of 2.5 nM and 30,000 sites/cell. Monolayers of MCF‐7 cells were similarly found to bind [125I]rTIMP‐2 with a K
d of 1.6 nM and 25,000 sites/cell. Specific binding of MMP‐2 alone to HT‐1080 cells was not observed; however, pro‐MMP‐2/TIMP‐2 complex was capable of binding to the surface of HT‐1080 cells in a TIMP‐2‐dependent manner. Binding of rTIMP‐2 was not competed by the presence of TIMP‐1. These results suggest that rTIMP‐2 alone binds directly to the cell surface of HT‐1080 and MCF‐7 cell lines, and TIMP‐2 is capable of localizing MMP‐2 to the surface of HT‐1080 cells via interaction with a specific binding site.
Low nidogen affinity of laminin‐5 can be attributed to two serine residues in EGF‐like motif γ2III4
Authors: Mayer Ulrike , Pöschl Ernst , Gerecke Donald R. , Wolfe Wagman D. , Burgeson Robert E. , Timpl Rupert
Published: April 2003

High affinity nidogen binding of laminin‐1 (chain composition α1β1γ1) has been previously mapped to a single EGF‐like motif γ1III4 of its γ1 chain. Two more isoforms, laminin‐5 (α3β3γ2) and laminin‐7 (α3β2γ1), show low and high binding activity, respectively, indicating that the γ2 chain is of low affinity. This was confirmed by recombinant production of the homologous EGF‐like motif γ2III4 of the γ2 chain, which has a 100,000‐fold lower binding activity than γ1III4. The crucial heptapeptide binding sequence Asn‐lle‐Asp‐Pro‐Asn‐Ala‐Val of γ1III4 is modified in γ2III4 by replacing both the central Asn and Val by Ser. Changing these replacements to Asn and Val by site‐directed mutagenesis enhanced the activity of γ2III4 to a level which was only 5‐fold lower than that of γ1III4. Despite their high sequence identity (77%) motifs γ1III4 and γ2III4 were also shown to differ considerably in immunological epitopes. This indicates distinctly different functions for laminins which differ in the γ chain isoform.
The tetracycline efflux protein encoded by the tet(K) gene from Staphylococcus aureus is a metal‐tetracycline/H+ antiporter
Authors: Yamaguchi Akihito , Shiina Yasuko , Fujihira Erika , Sawai Tetsuo , Noguchi Norihisa , Sasatsu Masanori
Published: April 2003

The tet(K) gene from Staphylococcus aureus was highly expressed in Escherichia coli by an alteration of its initiation codon from TTG to ATG and its ribosome‐binding sequence from GAGG to GGAGG [Noguchi, N. et al. (1994) Biol. Pharm. Bull. 17, 352–355]. The inverted membrane vesicles prepared from the tet(K)‐expressing cells showed respiration‐dependent [3H]tetracycline transport comparable to the vesicles from the tet(B)‐expressing cells. The affinity of Tet(K) vesicles to tetracycline was the same as that of Tet(B) vesicles, whereas the former V
max value was about 60% of the latter one. Contrary to Tet(B) vesicles, Tet(K) vesicles showed no significant minocycline uptake, which was consistent with the low minocycline resistance of the Tet(K)‐producing cells. The tetracycline transport mediated by Tet(K) vesicles was coupled with proton transport and the translocation of 60Co2+ ions as well as in Tet(B) vesicles. This observation indicates that the class K tetracycline resistance determinant from Gram‐positive bacteria also encodes a metaltetracycline/H+ antiporter that is functionally similar to that encoded by tet(B), although there is a considerable difference in the primary sequences and the putative topologies of these Tet proteins.
Almost the entire 5′ non‐translated region of hepatitis C virus is required for cap‐independent translation
Authors: Rijnbrand René , Bredenbeek Peter , van der Straaten Tahar , Whetter Linda , Inchauspé Geneviève , Lemon Stanley , Spaan Willy
Published: April 2003

To investigate which hairpin structures within the 5′ untranslated region of hepatitis C virus (HCV) are necessary for cap‐independent translation, mutants were constructed that lack one or more hairpin structures. Here we demonstrate, by constructing precisely defined hairpin deletion mutants, that with the exception of the most 5′ located hairpin structure, which on deletion shows an increase on translation, each of the predicted hairpins is found to be essential for cap‐independent translation. In addition, we demonstrate that HCV 5′UTR driven translation is stimulated by poliovirus 2Apro co‐expression.
Primary structure and expression of a novel human laminin α4 chain
Authors: Iivanainen Antti , Sainio Kirsi , Sariola Hannu , Tryggvason Karl
Published: April 2003

The complete primary structure of a novel human laminin α4 chain was derived from cDNA clones. The translation product contains a 24‐residue signal peptide preceding the mature α4 chain of 1792 residues. The domain structure is similar to that of the recently described α3 chain [Ryan, Tizard, Van Devanter and Carter (1994) J. Biol. Chem. 269, 22779–22787]. Northern analysis of RNA from human fetal and adult tissues revealed developmental regulation of expression. In adult, strong expression was observed in heart as well as lung, ovary, small and large intestines, placenta and liver, whereas weak or no expression was detected in skeletal muscle, kidney, pancreas, testis, prostate or brain. In contrast, fetal lung and kidney revealed high expression. In situ hybridization analysis of human fetal and newborn tissues showed expression of the laminin in α4 chain in certain mesenchymal cells in tissues such as smooth muscle and dermis.
Isoforms of 14‐3‐3 protein can form homo‐ and heterodimers in vivo and in vitro: implications for function as adapter proteins
Authors: Jones David H. , Ley Steven , Aitken Alastair
Published: April 2003

14‐3‐3 proteins play a role in many cellular functions: they bind to and regulate several proteins which are critical for cell proliferation and differentiation. 14‐3‐3 proteins exist as dimers, and in this study we have shown that diverse 14‐3‐3 proteins can form both homo‐ and heterodimers in vitro (by crosslinking studies) and in vivo (by coimmunoprecipitation and Western blot analysis); this interaction is mediated solely through the N‐terminal domain of the proteins. The composition of 14‐3‐3 dimers within a cell may play a key part in the role of this family of proteins as modulators or adapters which facilitate the interaction of distinct components of signalling pathways.
Oxidative stress response in yeast: effect of glutathione on adaptation to hydrogen peroxide stress in Saccharomyces cerevisiae
Authors: Izawa Shingo , Inoue Yoshiharu , Kimura Akira
Published: April 2003

Role of intracellular glutathione in the response of Saccharomyces cerevisiae to H2O2 was investigated. Depletion of cellular glutathione or inhibition of γ‐glutamylcysteine synthetase (GSH‐I) enhanced the sensitivity to H2O2 and suppressed the adaptation to H2O2. A mutant deficient in GSH‐I also showed the hypersensitivity and could not adapt to H2O2. Incubation of the cell with amino acids constituting glutathione (l‐Glu, l‐Cys, Gly) increased the intracellular glutathione content, and subsequently the cell acquired resistance against H2O2. These results strongly suggest that intracellular glutathione plays an important role in the adaptive response in S. cerevisiae to oxidative damage.
Long‐term enhancement of Na,K‐ATPase pump during blasttransformation of human lymphocytes is controlled first by translational, then by transcriptional mechanisms
Authors: Marakhova I.I. , Vereninov A.A. , Toropova F.V. , Vinogradova T.A.
Published: April 2003

The transition of phytohemagglutinin‐activated human lymphocytes from resting state to proliferation is accompanied by a long‐term increase in ouabain‐sensitive Rb(K) influx which is closely related to a cyclosporin A‐sensitive step of G0/G1/S progression. At least two distinct phases of the up‐regulation of cation pump has been revealed: the initial stage (5–20 h) which is cycloheximide‐inhibitable and actinomycin D (α‐amanitin)‐unaffected, and the later stage (after 20 h) which is cycloheximide‐ and actinomycin D (α‐amanitin)‐inhibitable. Thus, the enhanced Na,K‐ATPase pump during the cell progression from quiescence to proliferation is controlled both at translational and transcriptional levels.
Structure of an acidic polysaccharide present in the bacteriolytic complex lysoamidase
Authors: Likhosherstov Leonid M. , Senchenkova Sofya N. , Knirel Yuriy A. , Shashkov Alexander S. , Shibaev Vladimir N. , Stepnaya Olga A. , Kulaev Igor S.
Published: April 2003

The structure of an acidic polysaccharide component of a bacteriolytic complex (lysoamidase), isolated from a bacterium of the genus Xanthomonas, was studied. On the basis of sugar analysis and one‒ and two‒dimensional 1H and 13C NMR spectroscopic study of the initial polysaccharide and its O‒deacetylated and carboxyl‒reduced derivatives, the following structure of the trisaccharide repeating unit of the polysaccharide was established where ManNAcA and GalNAcA are 2‒acetamido‒2‒deoxymannuronic acid and 2‒acetamido‒2‒deoxygalacturonic acid, respectively.
Licorice‐derived compounds inhibit linoleic acid (C:18:2ω6) desaturation in soybean chloroplasts
Authors: Norman Helen A. , Pillai Parthasarathy , Baker Michael E.
Published: April 2003

Although glycyrrhizic acid, a major constituent of licorice root, has important pharmacological effects in humans, the biological activity of glycyrrhizic acid and its aglycone glycyrrhetinic acid in plants is unknown. Here we report that these licorice‐derived compounds and the analog carbenoxolone inhibit desaturation of linoleic acid (C18:2ω6) in soybean chloroplasts using monogalactosyldiacylglycerol and phosphatidylcholine substrates in an in vitro assay for desaturase activity. At 10 nM glycyrrhetinic acid, there is significant inhibition of desaturation of linoleic acid suggesting that licorice‐derived compounds could prove useful in investigating biochemical pathways of linoleic acid desaturation in plant chloroplasts and plant desaturase regulation, which has application in modification of plant response to environmental stress, as well as optimization of oil seed composition.
Insulin and insulin‐like growth factor I stimulate expression of the primary response gene cMG1/TIS11 b by a wortmannin‐sensitive pathway in RIE‐1 cells
Authors: Corps Anthony N. , Brown Kenneth D.
Published: April 2003

The addition of insulin or insulin‐like growth factor I (IGF‐I) to RIE‐1 cells increased the expression of the primary response gene cMG1; dose‐response analysis suggested that this effect was mediated largely through type 1 IGF receptors. Insulin/IGF‐I did not affect the expression of the cMG1‐related genes TIS11 and TIS11d, whereas epidermal growth factor, angiotensin II or 12‐O‐tetradecanoyl expression of all three genes. Incubation with wortmannin (WM) prevented the insulin/IGH‐I‐induced elevation of cMG1 mRNA, but not that induced by the other mitogens or the stimulation of mitogen‐activated protein kinase by insulin. We conclude that WM‐sensitive phosphatidylinositol 3‐kinase may be involved in the specific stimulation of cMG1 expression by insulin/IGF‐I.
NAD‐dependent methylenetetrahydrofolate dehydrogenase‐methenyltetrahydrofolate cyclohydrolase is targeted to the cytoplasm in insect cell lines
Authors: Tremblay Gilles B. , Sohi Sardar S. , Retnakaran Arthur , MacKenzie Robert E.
Published: April 2003

Cytosolic NADP‐dependent methylenetetrahydrofolate dehydrogenase‐cyclohydrolase synthetase and the mitochondrial NAD‐dependent methylenetetrahydrofolate dehydrogenase‐cyclohydrolase (NMDMC) are differentially expressed during insect development although both enzymes are detectable at all stages. In contrast, cell lines derived from a variety of insect species express high levels of NMDMC but undetectable levels of the NADP‐dependent enzyme. Northern analysis indicates the NMDMC message is expressed at levels 50–100 times higher in a Drosophila cell line compared to adult flies. RNase protection showed the predominance of shortened transcripts that require initiation at a downstream AUG producing a truncated protein that lacks a mitochondrial targeting sequence. These changes in expression effectively exchange the cytosolic NADP‐dependent dehydrogenase for one with NAD specificity.
Epidermal growth factor inhibits cytokine‐dependent nitric oxide synthase expression in hepatocytes
Authors: Terenzi Fulvia , Casado Marta , Martin-Sanz Paloma , Boscá Lisardo
Published: April 2003

Liver cells express a wide range of extracellular receptors involved in the control of cell growth and arrest that can be studied ex vivo. Incubation of primary cultures of hepatocytes with IL‐1β, TNF‐α or lipopolysaccharide promotes the expression of the inducible form of nitric oxide synthase and NO release, a process that is inhibited to a different extent by incubation of the cells with EGF. In addition to this growth factor, IL‐6 and TGF‐β also inhibited NO synthesis. Therefore, EGF by itself or in combination with other cytokines may be involved in the downregulation of the NO synthesis that occurs in the early steps of liver regeneration.
Nitric oxide induces intracellular Ca2+ mobilization and increases secretion of incorporated 5‐hydroxytryptamine in rat pancreatic β‐cells
Authors: Willmott Nicholas J. , Galione Antony , Smith Paul A.
Published: April 2003

This study is the first to demonstrate that low concentrations of aqueous NO induce intracellular Ca2+ mobilization and an increase in secretory activity of rat pancreatic β‐cells. Application of NO solution (2 μM) resulted in a transient increase in the free intracellular Ca2+ concentration ([Ca2+]i) of isolated cells, as assessed by video ratio imaging and single wavelength microfluorimetry. Amperometry revealed a simultaneous increase in the release of preloaded 5‐hydroxytryptamine from the isolated cells. The NO‐induced Ca2+ response primarily involves mobilization of endoplasmic reticulum Ca2+ stores, since the response was retained when cells were transferred to low Ca2+ medium, and completely inhibited when cells were pretreated with 10 μM thapsigargin. The Ca2+ response was also inhibited when cells were incubated with a high concentration of ryanodine (200 μM), suggesting that Ca2+ mobilization is via a ryanodine‐sensitive store.
Resistance against multiple plant viruses in plants mediated by a double stranded‐RNA specific ribonuclease
Authors: Watanabe Yuichiro , Ogawa Toshiya , Takahashi Hisae , Ishida Isao , Takeuchi Yoji , Yamamoto Masayuki , Okada Yoshimi
Published: April 2003

Many plant viruses have single‐stranded RNAs as their genomes. During the course of replication, genomic RNAs and their complementary template RNAs are likely to form double‐stranded (ds) RNA at least transiently. To attack replication intermediates of many plant RNA viruses specifically, we introduced a yeast‐derived ds‐RNA specific RNase gene called pac 1 into plants. The transformed plants showed a decrease in lesion numbers when they were challenged with tomato mosaic virus, and a delay in the appearance of symptoms when inoculated with cucumber mosaic virus or potato virus Y.
Wortmannin has opposite effects on phorbol ester‐induced DNA synthesis and phosphatidylcholine hydrolysis
Authors: Kiss Zoltan , Tomono Masahiro
Published: April 2003

The tumor promoter phorbol 12‐myristate 13‐acetate (PMA) and hormonal activators of protein kinase C (PKC) commonly stimulate phospholipase D (PLD)‐mediated formation of phosphatidic acid from phosphatidylcholine (PtdCho) in fibroblasts and other cell types. On the basis that phosphatidic acid is a mitogen, PLD is often considered to have a major role in the regulation of cell growth by PKC activators. However, we found that in NIH 3T3 fibroblasts wortmannin, an inhibitor of phosphatidylinositol 3‐kinase (P13K), strongly inhibited DNA synthesis induced by 100 nM PMA, while it actually enhanced PMA‐stimulated PtdCho hydrolysis. These results indicate that stimulation of PLD activity is either not required or not sufficient for the mitogenic action of PMA.
Using lipoate enantiomers and thioredoxin to study the mechanism of the 2‐oxoacid‐dependent dihydrolipoate production by the 2‐oxoacid dehydrogenase complexes
Authors: Bunik V. , Shoubnikova A. , Loeffelhardt S. , Bisswanger H. , Borbe H.O. , Follmann H.
Published: April 2003

The thioredoxin‐catalyzed insulin reduction by dihydrolipoate was applied to study the 2‐oxoacid:lipoate oxidoreductase activity of 2‐oxoacid dehydrogenase complexes. The enzymatic and non‐enzymatic mechanisms of the transfer of reducing equivalents from the complexes to free lipoic acid (α‐lipoic acid, 6,8‐thiooctic acid) were distinguished using the high stereoselectivity of the complex enzymes to the R‐enantiomer of lipoate. Unlike these enzymes, thioredoxin from E. coli exibited no stereoselectivity upon reduction with chemically obtained dihydrolipoate. However, coupled to the dihydrolipoate production by dehydrogenase complexes, the process was essentially sensitive both to the enantiomer used and the dihydrolipoyl dehydrogenase activity of the complexes. These results indicated the involvement of the third complex component, dihydrolipoyl dehydrogenase, in the 2‐oxoacid‐dependent dihydrolipoate formation. The implication of the investigated reaction for a connection between thioredoxin and the 2‐oxoacid dehydrogenase complexes in the mitochondrial metabolism are discussed.
Ultraviolet B irradiation increases endothelin‐1 and endothelin receptor expression in cultured human keratinocytes
Authors: Tsuboi Ryoji , Sato Chiyo , Oshita Yoshitami , Hama Hiroshi , Sakurai Takeshi , Goto Katsutoshi , Ogawa Hideoki
Published: April 2003

The effect of ultraviolet B (UVB) irradiation on endothelin‐1 (ET‐1) and ET receptor expression was examined using cultured normal human keratinocytes. Keratinocytes secreted ET‐1 in the medium at a level of 2.1 pg/day/105 cells. UVB irradiation up to 10 mJ/cm2 increased ET‐1 secretion 3‐fold, and potentiated expression of mRNA for ET‐1. Both ETA and ETB receptor mRNAs were detected in keratinocytes, and their expression was up‐regulated by 5 mJ/cm2 UVB irradiation.
Small‐angle X‐ray solution scattering study on the dimerization of the FKBP25mem from Legionella pneumophila
Authors: Schmidt Bettina , König Stephan , Svergun Dmitri , Volkov Vladimir , Fischer Gunter , Koch Michel H.J.
Published: April 2003

The dimerization of the FK506‐binding peptidyl‐prolyl cisltrans‐isomerase (PPIase) FKBP25mem (Mip (macrophage infectivity potentiator) protein) from Legionella pneumophila was studied by small‐angle X‐ray solution scattering. A value of 44 kDa, independent on the protein concentration between 2 and 13 mg/ml, confirming that FKBP25mem is a dimer was found for the molecular mass of the protein. The radius of gyration of the protein is 3.3 nm and the Porod volume 87 nm3. A model of the shape of FKBP25mem was evaluated from the scattering curve. Each monomer consists of a proximal and a peripheral domain, which are perpendicular to each other. The envelope of the crystallographic model of human FKBP12 fits well into the peripheral domain. The contact regions between the two monomers in the dimeric protein are probably located between the N‐terminal parts of the monomers.
A new hepatocyte stimulating factor: cardiotrophin‐1 (CT‐1)
Authors: Peters Malte , Roeb Elke , Pennica Diane , zum Büschenfelde Karl-Hermann Meyer , Rose-John Stefan
Published: April 2003

Recently, a novel cytokine, cardiotrophin‐1 (CT‐1), was cloned and found to induce cardiac myocyte hypertrophy in vitro. Amino acid sequence similarity showed CT‐1 to be a member of the IL‐6/LIF/CNTF/OSM/IL‐11 cytokine family. Since all known members of the IL‐6 cytokine family induce an hepatic acute phase protein (APP) gene expression, we investigated the ability of CT‐1 to induce a liver acute phase response. Upon stimulation of rat hepatoma cells, CT‐1 and LIF induced the strongest rat fibrinogen mRNA expression, OSM and IL‐6 induced a less pronounced response. When human hepatoma cells and primary rat hepatocytes were stimulated with CT‐1, the expression of human haptoglobin and rat α
2‐macroglobulin mRNA was induced. The induction of the acute phase response was dose‐ and time‐dependent. In this study we demonstrate that CT‐1, a novel cytokine belonging to the IL‐6 cytokine family, is a hepatocyte stimulating factor.
Hypoxia prolongs neutrophil survival in vitro
Authors: Hannah Sharon , Mecklenburgh Kathryn , Rahman Irfan , Bellingan Geoffrey J. , Greening Andrew , Haslett Christopher , Chilvers Edwin R.
Published: April 2003

Neutrophil apoptosis represents a major mechanism involved in the resolution of inflammation. Since hypoxia induces apoptosis in several cell lines and is of particular relevance in many disease states, we studied the effect of oxygen concentration on neutrophil survival in vitro. Hypoxia caused a dramatic decrease in neutrophil apoptosis (% apoptosis 20 h: 78.7 ± 2.2% in 21% O2, 61.4 ± 6.5% in 2.5% O2, 23.1 ± 3.2% in 0% O2, n = 5). This was additive to the effect of GM‐CSF (50 U/ml), not associated with induction of bcl‐2 expression, and was not mimicked by methionine (5 mM), superoxide dismutase (200 μg/ml) or Trolox (10 mM) but was mimicked by catalase (250 μg/ml). Hence, hypoxia has a bcl‐2‐independent effect on neutrophil appoptosis that may adversely affect the clearance of these cells from an inflammatory focus.
Salt‐stabilized globular protein structure in 7 M aqueous urea solution
Authors: Dötsch V. , Wider G. , Siegal G. , Wüthrich K.
Published: April 2003

A 7 M aqueous urea solution of the 63‐residue N‐terminal domain of the 434‐repressor at pH 7.5 and 18°C contains a mixture of about 10% native, folded protein and 90% unfolded protein. Interconversion between the two conformations is slow on the NMR chemical shift time scale, so that observation of separate resonances can be used to monitor the equilibrium between folded and unfolded protein when changing the solution conditions. In this paper we describe the influence of various salts or non‐ionic compounds on this conformational equilibrium. Solution conditions are described which contain a homogenous preparation of the folded protein in the presence of 6 to 7 M urea, providing a basis for an NMR structure determination in concentrated urea and for studies of the solvation of the folded protein in mixed water/urea/salt environments.
Oxidative DNA damage by t‐butyl hydroperoxide causes DNA single strand breaks which is not linked to cell lysis. A mechanistic study in freshly isolated rat hepatocytes
Authors: Latour I. , Demoulin J.B. , Buc-Calderon P.
Published: April 2003

In rat hepatocytes, DNA damage by t‐butyl hydroperoxide (tBOOH) was measured by using the fluorimetric analysis of alkaline DNA unwinding. The electrophoretic profile of genomic DNA suggests single rather than double DNA strand breaks formation. Oxidative DNA modifications, measured as increased 8‐hydroxy‐deoxyguanosine content, were not detected. Lysis of hepatocytes and DNA strand breaks induced by tBOOH did not correlate, indicating that both processes are not interconnected. Since o‐phenanthroline prevents against tBOOH‐mediated effects on both DNA and membrane integrity, we discussed about a putative role of iron.
Crystallization and crystallographic investigations of the small subunit of mouse ribonucleotide reductase
Authors: Nielsen Bettina Bryde , Kauppi Björn , Thelander Margareta , Thelander Lars , Larsen Ingrid Kjøller , Eklund Hans
Published: April 2003

The R2 protein component of mouse ribonucleotide reductase has been obtained from overproducing Escherichia coli bacteria. It has been crystallized using NaCl as precipitant. The crystals are orthorhombic, space group C2221 with cell dimensions and diffract to at least 2.5 Å. The asymmetric unit of the crystals contains one monomer. Rotation and translation function searches using a model based on the weakly homologous E. coli R2 gave one significant peak. Rotation about a crystallographic 2‐fold axis parallel to the a‐axis produces an R2 dimer with dimer interactions very similar to those found for E. coli R2.
Transition metal ions within human atherosclerotic lesions can catalyse the oxidation of low density lipoprotein by macrophages
Authors: Lamb David J. , Mitchinson Malcolm J. , Leake David S.
Published: April 2003

The oxidation of low density lipoprotein (LDL) in the arterial wall may contribute to atherogenesis. The oxidation of LDL by cells usually requires catalytically active transition metal ions. We show here some that gruel samples from human advanced atherosclerotic lesions are capable of catalysing the oxidation of LDL by macrophages as measured by thiobarbituric acid‐reactive substances, enhanced electrophoretic mobility and increased macrophage uptake. This catalysis could be inhibited by pretreatment of the gruel with Chelex‐100, which binds transition metal ions. The presence of catalytically active transition metal ions in atherosclerotic lesions may help to explain why LDL oxidation occurs at these sites.
Crystallization of threonyl‐tRNA synthetase from Thermus thermophilus and preliminary crystallographic data
Authors: Cura V. , Kern D. , Mitschler A. , Moras D.
Published: April 2003

Threonyl‐tRNA synthetase from Thermus thermophilus (ttTRS) has been overproduced in Escherichia coli, purified and crystallized in solutions containing ammonium sulfate and glycerol. The crystals grew in the orthorhombic space group C2221 with unit cell dimensions a = 119.5 Å, b = 120.0 Å, c = 317.5 Å. The asymmetric unit is constituted of two monomers and the crystals contain 66% solvent. This paper reports the first crystals of ttTRS and preliminary crystallographic results since the presumed crystals of ttTRS described in a previous paper [1] were crystals of aspartyl‐tRNA synthetase [2].
Factor VIIa and the extracellular domains of human tissue factor form a compact complex: A study by X‐ray and neutron solution scattering
Authors: Ashton Alun W. , Kemball-Cook Geoffrey , Johnson Daniel J.D. , Martin David M.A. , O'Brien Donogh P. , Tuddenham Edward G.D. , Perkins Stephen J.
Published: April 2003

The four‐domain structure of human factor VIIa and the two‐domain structure of tissue factor form a tight complex to initiate blood coagulation. By solution scattering, the mean X‐ray and neutron radii of gyration R
G (which determine macromolecular elongation) were found to be 3.25 nm, 2.13 nm and 3.14 nm (± 0.13 nm) for factor VIIa, the extracellular region of tissue factor and their complex in that order. The mean cross‐sectional radii of gyration R
XS were 1.33 nm, 0.56 nm and 1.42 nm (± 0.13 nm) in that order. The mean lengths were 10.3 nm, 7.7 nm and 10.2 nm in that order. The data show that, in solution, the free proteins have extended domain structures, and the complex is formed by a compact side‐by‐side alignment of the two proteins along their long axes. The high binding affinity of tissue factor for factor VIIa may thus be accounted for by the occurrence of many intermolecular contacts in the complex.
Expression of cDNA for a bark lectin of Robinia in transgenic tobacco plants
Authors: Tazaki Kiyoshi , Yoshida Kazumasa , Shinohara Kenji , Koshiba Tomokazu , Yamamoto Naoki
Published: April 2003

A cDNA encoding a bark lectin of Robinia pseudoacacia was introduced into tobacco plants. The expression of the lectin cDNA under control of the 35S promoter was confirmed by Western blot analysis and a hemagglutination assay of extracts of transgenic plants. Western blot analysis revealed that the subunit of the lectin from tobacco had a molecular mass of 29 kDa. The sequence of nine amino acids from the N‐terminus of the lectin from transgenic tobacco plants was identical to that of the bark lectin from Robinia, indicating that the lectin had been processed correctly at its N‐terminus in tobacco. The molecular mass of the purified native lectin produced by tobacco plants was estimated to be 112 kDa by gel filtration on a column of Superdex 200. It is suggested that the lectin subunits assembled to form tetramers in transgenic tobacco plants.
A three‐dimensional structure model of the complex of glutamyl‐tRNA synthetase and its cognate tRNA
Authors: Tateno Masaru , Nureki Osamu , Sekine Shun-ichi , Kaneda Kazuaki , G Mitiko , Yokoyama Shigeyuki
Published: April 2003

A docking model of glutamyl‐tRNA synthetase (GluRS) and tRNAGlu was constructed, on the basis of the distinguished similarity between the X‐ray crystallographic three‐dimensional structures of the N‐terminal halves of the Thermus thermophilus GluRS in the free state and the Escherichia coli glutaminyl‐tRNA synthetase in a complex with tRNAGln. The modeled structure is energetically favorable and is also well consistent with the results of site‐directed mutagenesis studies. The model indicates that the GluRS‐specific insertions 2 and 3 fit and bind to the acceptor stem and the D arm, respectively, of the cognate tRNA without affecting other contacts. In particular, insertion 3 strongly interacts with the two D‐stem base pairs that are essential for the tRNA·GluRS recognition.
The 65‐kDa protein derived from the internal translational start site of the clpA gene blocks autodegradation of ClpA by the ATP‐dependent protease Ti in Escherichia coli
Authors: Seol Jae Hong , Yoo Soon Ji , Kang Man-Sik , Ha Doo Bong , Chung Chin Ha
Published: April 2003

The ATP‐dependent protease Ti consists of two different components: ClpA containing ATP‐cleaving sites and ClpP having serine active sites for proteolysis. The clpA gene has dual translational start sites and therefore encodes two polypeptides with sizes of 84 and 65 kDa (referred to as ClpA84 and ClpA65, respectively). Here we show that ClpA84, but not ClpA65, is degraded in vitro by ClpP in the presence of ATP. The ClpP‐mediated hydrolysis of ClpA84 could be prevented by casein, which is an excellent substrate of protease Ti (i.e. ClpA84/ClpP complex). Thus, it appears that free form of ClpA84 competes with casein for the degradation by ClpA/ClpP complex. Furthermore, ClpA65 inhibited the auto‐degradation of ClpA84 by the complex. These results suggest that ClpA65 may play an important role in the control of the ClpA84 level and in turn in the regulation of ATP‐dependent protein breakdown in E. coli.
Characterization of multiple nicotinic acetylcholine receptor‐binding proteins and phospholipases A2 from the venom of the coral snake Micrurus nigrocinctus nigrocinctus
Authors: Alape-Girón Alberto , Stiles Bradley , Schmidt James , Girón-Cortes Mauricio , Thelestam Monica , Jörnvall Hans , Bergman Tomas
Published: April 2003

The presence of multiple nicotinic acetylcholine receptor (AchR)‐binding proteins and phospholipases A2 was detected in the venom of a member of the Elapinae subfamily, Micrurus nigrocinctus nigrocinctus. Multi‐step chromatographies were used to isolate four AchR‐binding proteins (Mnn‐9, Mnn‐4, Mnn‐3C and Mnn‐1A) and five basic PLA2s (nigroxins A, B, C1, C2 and C3). The Micrurus AchR‐binding proteins are antigenically and structurally related to short‐ and long‐chain α‐neurotoxins from Naja. The nigroxins are antigenically similar and constitute a new antigenic subclass of PLA2s. Nigroxins A and B are class I PLA2s, structurally more related to enzymes from Bungarinae than to those from Hydrophinae/Laticaudinae. These data contribute to clarify the relationships between Micrurus venom proteins and other elapid toxins and may be useful to improve the neutralizing efficiency of antivenoms.
An analysis of the conformational changes that accompany the activation and inhibition of gelatinase A
Authors: Crabbe Thomas , Kelly Sharon M. , Price Nicholas C.
Published: April 2003

The latent precursors of the matrix metalloproteinases (MMPs) are converted by (4‐aminophenylmercuric)acetate to active forms that lose their propeptide as a result of autolysis. C.D. and an active site mutant of progelatinase A (MMP2) were used to demonstrate that, although propeptide removal is accompanied by a decrease in the enzyme's β‐sheet content, the initial activation is achieved with only minor modifications to the conformation. Mixing activated gelatinase A with the natural inhibitor, TIMP‐1, resulted in conformational changes that were absent when a synthetic inhibitor was used. The relevance of these results to MMP activation and inhibition is discussed.
Diacylglycerol directly stimulates the insulin receptor tyrosine kinase
Authors: Arnold Rebecca S. , Newton Alexandra C.
Published: April 2003

Studies with detergent: lipid mixed micelles reveal that diacylglycerol directly stimulates the intrinsic tyrosine kinase activity of the insulin receptor. Kinetic analyses indicate that diacylglycerol activates the kinase by causing a marked increase in the affinity of the receptor for insulin. In contrast, diacylglycerol has no effect on the insulin receptor's catalytic activity or its affinity for ATP. Stimulation of the insulin receptor is not a result of protein kinase C activation. First, phorbol myristate acetate, a potent activator of protein kinase C, has no effect on insulin receptor activity. Second, the activation by diacylglycerol is not stereospecific, in marked contrast to the specificity for 1,2‐diacyl‐sn‐glycerol in the activation of protein kinase C. Because circulating levels of insulin are below the K
d of the insulin receptor forcor∗ insulin, the ability of diacylglycerol to modulate the affinity of the receptor for ligand suggests that increases in cellular levels of diacylglycerol directly sensitize the receptor to insulin.