bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolved lavas on Mars? Observations from southwest Arsia Mons and Sabancaya volcano, Peru
Authors: Warner Nicholas H. , Gregg Tracy K. P.
Published: October 2003

An extensive (106 km2) lava flow field SW of Arsia Mons contains individual lobes that are 102–103 km long, are ∼65 m thick, and display a surface ridging similar to the textures found on terrestrial andesite, dacite, and rhyolite flows, raising the question of whether large‐volume evolved lava flows exist on Mars. The regularly spaced ridges on these Martian flows have wavelengths of ∼100 ± 34 and amplitudes of ∼27 ± 11 m. An andesitic lava flow field at Sabancaya volcano, Peru, is a morphologic analog, with flow thicknesses of ∼60–170 m and surface ridges. One intensely studied flow lobe at Sabancaya has a ridge wavelength of ∼67 ± 24 m and amplitude of ∼5 ± 2 m. Despite morphologic similarities, comparing the calculated rheologic and emplacement parameters of the two lava flow fields reveals large differences. Calculated yield strengths for the Martian lavas are 103 Pa; those for lavas of Sabancaya, Peru, are 105 Pa. Effusion rates of 103–104 m3 s−1 calculated for the Martian flows are larger than those calculated for the Sabancaya lavas (1 m3 s−1). Calculations of emplacement times for the Martian and Sabancaya flows are 1–102 days and 1–103 days, respectively. Estimates of viscosity are 104–106 Pa s for southwestern Arsia Mons and 1010–1012 Pa s for Sabancaya. We therefore conclude that the flows southwest of Arsia Mons are most likely not the same composition as those at Sabancaya volcano, but rather are basaltic or basaltic andesite in composition.
Possible Juventae Chasma subice volcanic eruptions and Maja Valles ice outburst floods on Mars: Implications of Mars Global Surveyor crater densities, geomorphology, and topography
Authors: Chapman Mary G. , Gudmundsson Magnús T. , Russell Andrew J. , Hare Trent M.
Published: October 2003

This article discusses image, topographic, and spectral data from the Mars Global Surveyor (MGS) mission that provide new information concerning the surface age, geomorphology, and topography of the Juventae Chasma/Maja Valles system. Our study utilizes data from two instruments on board MGS: images from the Mars Orbiter Camera (MOC) and topography from the Mars Orbiter Laser Altimeter (MOLA). Within Maja Valles we can now observe depositional bars with megaripples that unequivocally show catastrophic floods occurred in the channel. Viking impact crater densities indicated the chasma and channel floor areas were all one age (late Hesperian to Amazonian); however, MOC data indicate a marked difference in densities of small craters between Juventae Chasma, Maja Valles, and the channel debouchment area in Chryse Planitia basin. Although other processes may contribute to crater variability, young resurfacing events in the chasma and episodes of recent erosion at Maja Valles channel head may possibly account for the disparate crater densities along the chasma/channel system. Relatively young volcanic eruptions may have contributed to resurfacing; as in Juventae Chasma, a small possible volcanic cone of young dark material is observed. MOC data also indicate previously unknown interior layered deposit mounds in the chasma that indicate at least two periods of mound formation. Finally, MOLA topography shows that the entire floor of the chasma lies at the same elevation as the channel debouchment area in Chryse basin, resulting in a 3‐km‐high barrier to water flow out of the chasma. Blocked ponded water would rapidly freeze in the current (and likely past) climate of Mars. For catastrophic flow to occur in Maja Valles, some process is required to melt ice and induce floods out of the chasma. We suggest subice volcanic eruption and calculate estimates of water discharges and volumes that these eruptions might have produced.
Radio wave propagation in the presence of a coastline
Authors: Casciato Mark D. , Oveisgharan Shadi , Sarabandi Kamal
Published: October 2003

In this paper the effect of a coastline on radio wave propagation is analyzed. The coastline consists of a shoreline or land/sea transition in the presence of a cliff or bluff. The problem of diffraction from the transition, when excited by a small dipole, is first addressed. By application of a perturbation technique the effects of a gradual, as opposed to an abrupt transition on the radio wave are discussed. For the case of both source and observation near the surface it is shown that the received fields are independent of the gradient of the transition and that the effects of the land/sea transition on the total fields are dominant, even distant from the transition. This is a very important and counter‐intuitive result which has not been reported previously. A UTD solution for an impedance wedge and plane wave excitation is then applied, in order to analyze the combined effect of the land/sea transition and a cliff or bluff on the total received fields. Results are shown for the case of an observation platform (such as an aerial vehicle) flying low over the sea and then up and over the bluff.
Radio wave propagation through vegetation: Factors influencing signal attenuation
Authors: Savage Nick , Ndzi David , Seville Andrew , Vilar Enric , Austin John
Published: October 2003

The paper describes an extensive wideband channel sounding measurement campaign to investigate signal propagation through vegetation. The measurements have been conducted at three frequencies (1.3, 2 and 11.6 GHz) at sites with different measurement geometries and tree species. The data have been used to evaluate current narrowband empirical vegetation attenuation models and study the prevailing propagation mechanisms. Evaluation of the modified exponential decay (MED), maximum attenuation (MA) and nonzero gradient (NZG) models show that on a site by site basis, the NZG model gives the best prediction of excess attenuation due to vegetation. The MA model has been found to be the worst of the three models. The studies have shown that the measurement site used to obtain the NZG model parameter values given in International Telecommunication Union (ITU) [2001] is influenced by metal lampposts and passing traffic, and thus was based on corrupted data. The results show that the leaf state, measurement geometry and vegetation density are more important factors influencing signal attenuation than tree species or leaf shape. Generally, the 11.6 GHz signal was attenuated much more than the 1.3 and 2 GHz signals by vegetation in‐leaf, but the differences in attenuation were not significant in the out‐of‐leaf state. A successful excess attenuation model due to vegetation must consider the measurement geometry and vegetation descriptive parameters as well as any contributions from ground reflection and/or diffraction over the top or round edges of the trees.
Tight coupling between soil moisture and the surface radiation budget in semiarid environments: Implications for land‐atmosphere interactions
Authors: Small Eric E. , Kurc Shirley A.
Published: October 2003

Observations are used to examine how soil moisture influences the surface radiation budget, ground heat flux, and available energy in semiarid environments. Defining this relationship is critical to understand interactions between the land surface and the atmosphere, in particular assessing if a feedback exists between soil moisture and rainfall anomalies. We use two summers of data collected from semiarid grassland and shrubland ecosystems in central New Mexico. The response of surface radiation budget components and other variables to soil moisture variations are quantified via linear regression. Then, the variations are scaled over the observed range of soil moisture (15% volumetric water content). The soil temperature is lower by >10°C when the surface soil is wet, compared to when the soil is dry. This temperature decrease results in a measured decrease of 85–100 W m−2 in longwave radiation emitted at the surface. The increase in net longwave radiation is equal in magnitude because downward longwave radiation does not vary with soil moisture. The observed changes in net shortwave radiation are relatively minor (<10 W m−2), as the surface albedo decreases by only 1.5% when soil is wet. Net radiation increases by an amount roughly equal to the decrease in emitted longwave radiation (∼85–100 W m−2). Changes in ground heat flux are not detectable, given the noise in the data. Therefore the available energy, Qa, is higher by 80 W m−2 when the soil is wet. This change is 22% of average Qa at the shrubland site and 19% at the grassland site. The observed soil moisture‐induced Qa variations are large compared to other sources of Qa variability, so they should influence boundary layer moist static energy. However, the intervals during which soil moisture is high and therefore Rn and Qa are enhanced are short, on the order of several days. Therefore feedbacks to rainfall may be limited. Compared to other environments, the influence of soil moisture on Rn and Qa is likely greater in semiarid environments because soil moisture‐induced fluctuations in evaporative fraction and surface temperature are relatively large.
Temporal dynamics of soil moisture variability: 1. Theoretical basis
Authors: Albertson John D. , Montaldo Nicola
Published: October 2003

Coarse soil moisture fields and nonlinear relationships between fluxes and soil moisture combine to yield errors in both diagnostic and predictive estimates of large‐scale mass and energy fluxes. Efforts to empirically define the dynamics of subgrid spatial variance of soil moisture have led to contradictory results. Moreover, most reports of soil moisture variability range from qualitative to descriptively quantitative, owing to the lack of a robust theoretical framework for moisture variance dynamics. In this paper we derive a conservation equation for the spatial variance of subgrid root zone soil moisture, based on first principles of statistical fluid mechanics. We arrive at a variance budget in which explicit covariances between moisture fields and land surface flux fields act to produce or destroy variance through time (according to the sign of the correlation between the flux and state fields). A series of examples are used to explore how simple forms of soil, vegetation, precipitation, topography, and initial moisture variability lead to evolving covariances between spatial fields of soil moisture and particular land surface fluxes and how these covariances relate to the temporal trajectory of the spatial variance of soil moisture. We isolate a set of processes and conditions that demonstrate variance production through time and a set that demonstrate variance destruction. Of particular interest is the tendency for transpiration and infiltration‐runoff processes to either produce or destroy variance, depending on the background wetness regime. Field data are also employed and shown to demonstrate a temporal behavior of the spatial variance that is readily described by the proposed approach. Ultimately, this work should aid field data interpretation and, when supplemented with a closure model for the variance budget, lead to improved land surface flux predictability over coarse grids.
Temporal dynamics of soil moisture variability: 2. Implications for land surface models
Authors: Montaldo Nicola , Albertson John D.
Published: October 2003

Given that land surface processes most often depend nonlinearly on soil moisture and that coarse‐grained soil moisture fields are often used in modern large‐scale applications, it becomes necessary to account in some way for the subgrid variability of physiographic properties and their interactions with subgrid soil moisture dynamics in order to derive robust estimates of grid‐scale land surface fluxes. Albertson and Montaldo [2003] present a conservation equation for subgrid soil moisture spatial variability, which includes production and destruction terms related to the various interactions between moisture fields and flux fields (i.e., infiltration, drainage, evapotranspiration, and horizontal redistribution). Here we present a rigorous closure of the conservation equations of the first and second moments of the soil moisture field (omitting topographic redistribution in this effort). Closed terms include correlation coefficients between soil moisture and physiographic properties. The approach presented here provides accounting for the effects of dynamic interaction between soil moisture spatial variability and the underlying soil texture and vegetation density fields. Closure is achieved in terms of the spatial mean soil moisture evolution, with closure coefficients being functions of the correlation coefficient between the underlying soil texture and vegetation density patterns (i.e., the physiographic setting). Making use of these relationships, the proposed approach uses known subgrid soil texture and vegetation density fields to accurately simulate the temporal trajectory of subgrid variance of soil moisture, which supports improved estimates of grid‐scale land surface fluxes. The approach is tested synthetically (closure model versus distributed model) over a wide range of physiographic characteristics and meteorological conditions, with results demonstrating that the closure model based approach reproduces the temporal dynamics of the soil moisture variability and provides improved grid‐scale land surface flux estimates. In fact, the second‐order closure was shown to reduce the errors in integrated land surface flux estimates, as compared to those derived from zero‐order approximation estimates, by an order of magnitude in certain conditions.
Upscaling of fracture hydraulics by means of an oriented correlated stochastic continuum model
Authors: Öhman Johan , Niemi Auli
Published: October 2003

Two methods for upscaling hydraulics of fractured media are compared, namely, a classical fracture network based approach and a new enhanced stochastic continuum approach, the benefit of the latter being that while avoiding some of the complexities of fracture network models, it still can describe strong heterogeneity better than a classical stochastic continuum approach. In the continuum approach the fracture‐induced heterogeneity is taken into account through an oriented, conductivity‐dependent correlation structure. In addition, the radius of influence of the well tests is considered when assigning input conductivity statistics. The best fitting correlation structure of the continuum model is determined based on how well the results from the fracture network model can be reproduced. The results show that this best fitting correlation structure closely resembles in shape the probability distribution of fracture transmissivities. In other words, in the conductivity range where there is a large number of fractures in the fracture network model, large correlation lengths should be used in the stochastic continuum model, while the conductivity ranges with few fractures correspond to small correlation lengths in the stochastic continuum model.
Identification and parameterization of flow processes in artificial capillary barriers
Authors: Kämpf M. , Holfelder T. , Montenegro H.
Published: October 2003

Capillary barriers have increased in use for protecting sensitive underground regions from downward infiltration. However, questions and uncertainties remain about conceptualization and parameterization of capillary barriers for design and numerical modeling. In order to identify and to parameterize the relevant flow processes in this fine‐over‐coarse soil layer system, large‐scale laboratory experiments were performed. The data revealed that water is predominately diverted laterally in a saturated fringe within the fine layer. Percolation through the system was found to be quite complex. At low infiltration rates, small quantities of water seeped uniformly through the system. At higher fluxes the seepage pattern changed to a more irregular distribution because of the occurrence of preferential flow. Numerical investigations based on the laboratory results demonstrated an extreme sensitivity of the system performance to the hydraulic functions of both layers.
Crustal motion in the Southern Andes (26°–36°S): Do the Andes behave like a microplate?
Authors: Brooks Benjamin A. , Bevis Michael , Smalley Robert , Kendrick Eric , Manceda René , Lauría Eduardo , Maturana Rodrigo , Araujo Mario
Published: October 2003

A new Global Positioning System (GPS)‐derived velocity field for the Andes mountains (26°–36°S) allows analysis of instantaneous partitioning between elastic and anelastic deformation at the orogen's opposing sides. Adding an “Andes” microplate to the traditional description of Nazca‐South America plate convergence provides the kinematic framework for nearly complete explanation of the observed velocity field. The results suggest the oceanic Nazca boundary is fully locked while the continental backarc boundary creeps continuously at ∼4.5 mm/yr. The excellent fit of model to data (1.7 mm/yr RMS velocity misfit), and the relative aseismicity of the upper crust in the interior Andean region in comparison with its boundaries, supports the notion that the mountains are not currently accruing significant permanent strains. Additionally, the model implies permanent deformation is not accumulating throughout the backarc contractional wedge, but rather that the deformation is accommodated only within a narrow deformational zone in the backarc.
On the relationship between stomatal characters and atmospheric CO2
Authors: Reid Chantal D. , Maherali Hafiz , Johnson Hyrum B. , Smith Stanley D. , Wullschleger Stan D. , Jackson Robert B.
Published: October 2003

Leaf stomatal characters influence the response of terrestrial evapotranspiration to climate change and are used as proxies for the reconstruction of past atmospheric [CO2]. We examined the phenotypic response of stomatal index (SI), density (SD) and aperture (AP) to rising atmospheric CO2 in 15 species after four years exposure to a field CO2 gradient (200 to 550 μmol mol−1 atmospheric [CO2]) or at three Free Air CO2 Enrichment (FACE) sites. Along the CO2 gradient, SI and SD showed no evidence of a decline to increasing [CO2], while AP decreased slightly. There was no significant change in SI, SD or AP with CO2 across FACE experiments. Without evolutionary changes, SI and SD may not respond to atmospheric [CO2] in the field and are unlikely to decrease in a future high CO2 world.
Utilizing riometry to observe gravity waves in the sunlit mesosphere
Authors: Jarvis M. J. , Hibbins R. E. , Taylor M. J. , Rosenberg T. J.
Published: October 2003

The novel use of imaging riometers to observe mesospheric gravity waves is described. Imaging riometers respond to changes in the absorption of cosmic radio noise in the ionospheric D‐region which enables them to detect the compression and rarefaction of the atmosphere at ∼90 km altitude generated by the passage of gravity waves. A considerable advantage of this method is that, unlike conventional techniques which rely on imaging faint optical emissions from the airglow layer at ∼87 km altitude, riometers remain operative under daylit, moonlit or cloudy conditions. This is particularly important for research into gravity wave forcing of mesospheric temperature at polar latitudes in summer when continuous 24‐hour daylight prevails. An example in which the same wave event is characterized in co‐located airglow imager and imaging riometer shows good agreement between the two instruments.
Causes and development of repeated Arctic Ocean warming events
Authors: Gerdes Rüdiger , Karcher Michael J. , Kauker Frank , Schauer Ursula
Published: October 2003

A model hindcast for 1948–2002 shows several warming events in the Atlantic layer of the Arctic Ocean. The most recent warming event in the 1990s spread from Fram Strait to the Lomonosov Ridge and into the Canadian Basin. Only a warming event in the 1960s can also be followed into the eastern Eurasian Basin. These two warming events are reinforced by anomalously warm flow from the Barents Sea while warming events in the 1970s and 1980s encounter average or below normal temperatures in the Barents Sea branch of the Atlantic Water. The warm Barents Sea outflow in the 1960s is caused by extensive ice cover and a melt water induced halocline in the Barents Sea that reduced heat loss from the Atlantic water. In the 1990s, however, the warm inflow from the Nordic Seas was responsible for warmer than normal flow from the Barents Sea into the Arctic Ocean.
Improved inversion for seismic structure using transformed, S‐wavevector receiver functions: Removing the effect of the free surface
Authors: Reading Anya , Kennett Brian , Sambridge Malcolm
Published: October 2003

The determination of structure from the inversion of teleseismic receiver functions may be improved by removing the contribution of the free surface. The free surface interaction gives rise to the highest amplitude signal on standard receiver functions and yet this initial pulse tells us little about the receiver structure below the surface layer. We apply a transformation to P, S and Horizontal wavevector components, which removes the free surface response and hence the initial P‐pulse. A “pure” receiver function is calculated by deconvolving the S‐wavevector component with the P‐wavevector. In general, converted phase amplitudes within the receiver function waveform are better matched by the inverse algorithm, resulting in an improved estimation of seismic structure. In particular, low amplitude receiver function waveforms, often associated with poorly constrained structure, now yield a successful inverse.
The effect of shearing on the onset and vigor of small‐scale convection in a Newtonian rheology
Authors: van Hunen Jeroen , Huang Jinshui , Zhong Shijie
Published: October 2003

As an oceanic plate cools with time, the bottom part of the plate may undergo gravitational instabilities and lead to sub‐lithospheric small‐scale convection (SSC). While numerous previous studies have examined the dynamics of SSC below a fixed top boundary, in this study we investigate the effects of shearing due to plate motion on the onset and time evolution of SSC with 2‐D and 3‐D finite element models with a prescribed surface plate motion and a Newtonian rheology. Our 3‐D models show that plate motion moderately enhances the SSC that displays plate‐motion‐parallel convective roll‐structures. However, plate motion significantly hinders SSC in 2‐D models with plate motion that produces plate‐motion‐perpendicular convective roll‐structures. In spite of moderate influences of plate motion on the dynamics of SSC, our results suggest that for Newtonian rheology the onset time of SSC predicted from previous studies with a fixed top boundary is to the first order valid.
Sea ice velocity in the Fram Strait monitored by moored instruments
Authors: Widell K. , Østerhus S. , Gammelsrød T.
Published: October 2003

The Fram Strait sea ice velocity was measured by means of a new method using moored Doppler Current Meters in the period 1996–2000. Almost 3 years of ice velocity observations near 79°N 5°W are analyzed. The average southward ice velocity was 0.16 m/s. The correlation between the ice velocity and the cross‐strait sea level pressure (SLP) difference was R = 0.76 for daily means and R = 0.79 for monthly means. The same cross‐strait SLP difference exhibits a positive trend since 1950 of 10% of the mean per decade. By a simple linear model we compute mean sea ice area flux to 850 000 km2/year for the period 1950–2000. Ice thickness, monitored by means of Upward Looking Sonars since 1990, is also discussed. The combined data gave a monthly ice volume flux of 200 km3 during the last decade with no significant trend.
Atmospheric methane levels off: Temporary pause or a new steady‐state?
Authors: Dlugokencky E. J. , Houweling S. , Bruhwiler L. , Masarie K. A. , Lang P. M. , Miller J. B. , Tans P. P.
Published: October 2003

The globally‐averaged atmospheric methane abundance determined from an extensive network of surface air sampling sites was constant at ∼1751 ppb from 1999 through 2002. Assuming that the methane lifetime has been constant, this implies that during this 4‐year period the global methane budget has been at steady state. We also observed a significant decrease in the difference between northern and southern polar zonal annual averages of CH4 from 1991 to 1992. Using a 3‐D transport model, we show that this change is consistent with a decrease in CH4 emissions of ∼10 Tg CH4 from north of 50°N in the early‐1990s. This decrease in emissions may have accelerated the global methane budget towards steady state. Based on current knowledge of the global methane budget and how it has changed with time, it is not possible to tell if the atmospheric methane burden has peaked, or if we are only observing a persistent, but temporary pause in its increase.
Detection of thin cirrus from 1.38 μm/0.65 μm reflectance ratio combined with 8.6–11 μm brightness temperature difference
Authors: Roskovensky J. K. , Liou K. N.
Published: October 2003

We developed a new detection scheme for the identification of thin cirrus based on a combination of the 1.38 μm and 0.65 μm reflectance ratio and 8.6–11 μm brightness temperature difference. Results computed from a radiative transfer model as well as data obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra satellite were used to demonstrate the applicability of this method for regional mapping of thin cirrus. The mm‐wave radar backscatter data, coincident and collocated with MODIS data, available from the DOE's Atmospheric Radiation Measurement (ARM) sites, was employed for validation of the present satellite detection results. In all cases selected, our new method was able to detect the majority of thin cirrus estimated to have optical thickness between 0.1 and 0.9. It also compared favorably to existing detection tests.
The origin of teleseismic Pn waves: Multiple crustal scattering of upper mantle whispering gallery phases
Authors: Nielsen L. , Thybo H.
Published: October 2003

Teleseismic Pn arrivals with an extensive coda are observed to offsets beyond 3000 km along the peaceful nuclear explosion seismic profiles Quartz and Ruby, which were recorded in the western part of the former Soviet Union. We interpret these arrivals as multiply reflected sub‐Moho refractions that travel over large distances due to a positive vertical upper mantle velocity gradient, which is characteristic for the study area. Analysis of the observed data shows that the teleseismic Pn and its coda contain significant amounts of energy at all frequencies between 0 and 10 Hz. Our modeling results show that crustal scattering may fully explain the teleseismic Pn coda contrary to another published model with upper mantle heterogeneity in the ∼35–130 km depth range. These conclusions are based on two‐dimensional viscoelastic finite‐difference seismic wave field simulations in 2000‐km‐long and 250‐km‐deep models of the crust and upper mantle. The computationally demanding calculations are facilitated by the use of supercomputer systems. Our preferred model of crustal scattering is consistent with the results of other high‐resolution wide‐angle and normal‐incidence seismic investigations of the crust and upper mantle. They show pronounced reflectivity of the lower crust above an almost transparent uppermost mantle down to ∼80–100 km depth. Our model includes a high vertical velocity gradient in the upper mantle based on the results from seismic refraction studies. We suggest that the teleseismic Pn wave travels as an upper mantle whispering gallery phase and that the origin of its long coda is crustal scattering.
Climate stability during the Pliocene warm period
Authors: Draut Amy E. , Raymo Maureen E. , McManus Jerry F. , Oppo Delia W.
Published: October 2003

We present a high‐resolution climate record from a sediment core spanning an 80‐kyr interval of time during the mid‐Pliocene epoch, when warmer conditions and lower global ice volume prevailed worldwide. Oxygen and carbon isotope analyses were made on benthic and planktonic foraminifera from ODP Site 981 in the North Atlantic. The amplitude and approximate recurrence interval of suborbital variations in these records are comparable to those of Holocene and marine isotope stage 11 (MIS 11) records from the North Atlantic. We conclude that the mid‐Pliocene warm interval was a time of relative climatic stability. These results suggest that warmer climatic conditions alone may not necessarily enhance variability in the climate system, a finding that may facilitate predictions of 21st century climatic response to anthropogenic warming.
The ribosome and YidC
Authors: de Gier Jan‐Willem L , Luirink Joen
Published: October 2003

In the bacterium Escherichia coli, inner membrane proteins (IMPs) are generally targeted through the signal recognition particle pathway to the Sec translocon, which is capable of both linear transport into the periplasm and lateral transport into the lipid bilayer. Lateral transport seems to be assisted by the IMP YidC. In this article, we discuss recent observations that point to a key role for the ribosome in IMP targeting and to the diverse roles of YidC in IMP assembly.
Finding the right organelle
Authors: Rapaport Doron
Published: October 2003

The mitochondrial outer membrane contains a diverse set of proteins that includes enzymes, components of the preprotein translocation machinery, pore‐forming proteins, regulators of programmed cell death, and those that control the morphology of the organelle. All these proteins, like the vast majority of mitochondrial proteins, are encoded in the nucleus, so they are synthesized in the cytosol and contain signals that are essential for their subsequent import into mitochondria. This review summarizes our current knowledge of the signals that target mitochondrial outer‐membrane proteins to their correct intracellular location. In addition, the mechanisms by which these signals are decoded by the mitochondria are discussed.
An essential function of the mitogen‐activated protein kinase Erk2 in mouse trophoblast development
Authors: Saba‐El‐Leil Marc K , Vella Francis D J , Vernay Bertrand , Voisin Laure , Chen Lan , Labrecque Nathalie , Ang Siew‐Lan , Meloche Sylvain
Published: October 2003

The closely related mitogen‐activated protein kinase isoforms extracellular signal‐regulated kinase 1 (ERK1) and ERK2 have been implicated in the control of cell proliferation, differentiation and survival. However, the specific in vivo functions of the two ERK isoforms remain to be analysed. Here, we show that disruption of the Erk2 locus leads to embryonic lethality early in mouse development after the implantation stage. Erk2 mutant embryos fail to form the ectoplacental cone and extra‐embryonic ectoderm, which give rise to mature trophoblast derivatives in the fetus. Analysis of chimeric embryos showed that Erk2 functions in a cell‐autonomous manner during the development of extra‐embryonic cell lineages. We also found that both Erk2 and Erk1 are widely expressed throughout early‐stage embryos. The inability of Erk1 to compensate for Erk2 function suggests a specific function for Erk2 in normal trophoblast development in the mouse, probably in regulating the proliferation of polar trophectoderm cells.
Regulating histone acetyltransferases and deacetylases
Authors: Legube Gaëlle , Trouche Didier
Published: October 2003

Histone acetyltransferases and histone deacetylases regulate the acetylation of histones and transcription factors, and in doing so have major roles in the control of cell fate. Many recent results have indicated that their function is strictly regulated in cells through the modulation of their levels, activity and availability for interaction with specific transcription factors. In this review, we present the various molecular mechanisms that bring about this tight regulation and discuss how these regulatory events influence cellular responses to environmental changes.
Spatiotemporal dynamics of the COPI vesicle machinery
Authors: Elsner Markus , Hashimoto Hitoshi , Simpson Jeremy C , Cassel Dan , Nilsson Tommy , Weiss Matthias
Published: October 2003

Assembly of the coat protein I (COPI) vesicle coat is controlled by the small GTPase ADP ribosylation factor 1 (ARF1) and its GTPase‐activating protein, ARFGAP1. Here, we investigate the diffusional behaviours of coatomer, the main component of the coat, and also those of ARF1 and ARFGAP1. Using fluorescence‐correlation spectroscopy, we found that most ARF1 and ARFGAP1 molecules are highly mobile in the cytosol (diffusion constant D ≈ 15 μm2 s−1), whereas coatomer diffuses 5–10 times more slowly than expected (D ≈ 1 μm2 s−1). This slow diffusion causes diffusion‐limited binding kinetics to Golgi membranes, which, in FRAP (fluorescence recovery after photobleaching) experiments, translates into a twofold slower binding rate. The addition of aluminium fluoride locks coatomer onto Golgi membranes and also decreases the binding kinetics of both ARF1 and ARFGAP1, suggesting that these proteins function in concert to mediate sorting and vesicle formation.
Adenovirus protein IX sequesters host‐cell promyelocytic leukaemia protein and contributes to efficient viral proliferation
Authors: Rosa‐Calatrava Manuel , Puvion‐Dutilleul Francine , Lutz Pierre , Dreyer Dominique , De Thé Hugues , Chatton Bruno , Kedinger Claude
Published: October 2003

The product of adenovirus type 5 (Ad5) gene IX, protein IX (pIX), is a multifunctional protein that stabilizes the viral capsid and has transcriptional activity. We show that pIX also contributes to the Ad5‐induced reorganization of the host‐cell nuclear ultrastructure: pIX induces the formation of specific and dynamic nuclear inclusions, and the host promyelocytic leukaemia (PML) protein, which is the main structural organizer of PML bodies, is stably relocated and confined within the pIX‐induced inclusions late in infection. Our results suggest that Ad5 has evolved a unique strategy that leads to the sustained neutralization of PML bodies throughout infection, thereby ensuring optimal viral proliferation.
Exclusion of exogenous phosphatidylinositol‐3,4,5‐trisphosphate from neutrophil‐polarizing pseudopodia: stabilization of the uropod and cell polarity
Authors: Tian Wei , Laffafian Iraj , Dewitt Sharon , Hallett Maurice B
Published: October 2003

Although there is accumulating evidence that the generation and localization of phosphatidylinositol‐3,4,5‐trisphosphate (PtdIns(3,4,5)P3) have important functions in neutrophil polarization and chemotaxis, the mechanism of this linkage has yet to be established. Here, using exogenous fluorescent PtdIns(3,4,5)P3 introduced into the inner leaflet of the neutrophil plasma membrane by a cationic carrier, we show that: first, PtdIns(3,4,5)P3 uniformly delivered to the neutrophil plasma membrane is excluded from newly forming pseudopodia; second, PtdIns(3,4,5)P3 translocates to and is immobilized at the pole opposite a stable polarizing pseudopod; third, asymmetric delivery of PtdIns(3,4,5)P3 to the neutrophil triggers the generation of polarizing pseudopodia at the opposite pole; and finally, PtdIns(3,4,5)P3 triggers repetitive Ca2+ signals, the onset of which precedes morphological polarization. These data suggest that translocation and immobilization of PtdIns(3,4,5)P3 or a 3,x‐phosphorylated metabolite in the uropod functions as an important polarization cue that defines neutrophil polarity and stabilizes the generation of pseudopodia at the opposite pole.
A novel method for the immobilization of tyrosinase to enhance stability
Authors: Sharma Neeru Munjal , Kumar Sushil , Sawhney Suriender Kumar
Published: October 2003

A new method of tyrosinase immobilization by Fuller's‐earth adsorption followed by entrapment in gelatin has been developed with 98% activity immobilization yield. An appreciable increase in operational and thermal stability was observed for FEAGE (Fuller's earth‐adsorbed gelatin‐entrapped) tyrosinase compared with GE (gelatin‐entrapped) native enzyme. FEAGE tyrosinase could be used repeatedly after intermittent storage and retained 70% of its initial activity after eight cycles. The half‐life of the GE enzyme at 40 °C was less than 2 h, whereas the FEAGE enzyme retained about 75% of its initial activity after 2 h. Taken together our data demonstrate clearly that the technique of immobilizing tyrosinase via adsorption followed by entrapment appears promising and is hence recommended for tyrosinase immobilization for commercial production of l‐DOPA (3,4‐dihydroxyphenylalanine).
Enhanced expression of the gene for β‐glycosidase ofThermus caldophilusGK24 and synthesis of galacto‐oligosaccharides by the enzyme
Authors: Choi Jeong Jin , Oh Eun‐Joo , Lee Yoon‐Jin , Suh Dong Sang , Lee Jae Heung , Lee Soo‐Won , Shin Hyung‐Tai , Kwon Suk‐Tae
Published: October 2003

The gene (bglT) encodingTcaβ‐glycosidase (Thermus caldophilusGK24 β‐glycosidase) was overexpressed under the control of thetrppromoter on a high‐copy‐number plasmid, pTRPES, inEscherichia coliW3110. The purifiedTcaβ‐glycosidase enzyme was used in a galactosyl‐transfer reaction to synthesize galacto‐oligosaccharides from lactose. The optimum temperature and pH for the enzyme to synthesize galacto‐oligosaccharides from 30% (w/v) lactose were 80 °C and 6.0, respectively. The major product of the reaction was a trisaccharide. The thermostableTcaβ‐glycosidase produced galacto‐oligosaccharides efficiently during the hydrolysis of lactose.
Nucleoside diphosphate kinase‐like activity in adenylate kinase of Mycobacterium tuberculosis
Authors: Meena Laxman S. , Chopra Puneet , Bedwal R. S. , Singh Yogendra
Published: October 2003

Ak (adenylate kinase) is a ubiquitous enzyme that catalyses a reversible high‐energy phosphoryl‐transfer reaction between ATP and AMP to form ADP. In the present study, the Ak gene (adk) of Mycobacterium tuberculosis was cloned, expressed in Escherichia coli and purified as a glutathione S‐transferase fusion protein. Purified Ak converted AMP into ADP in the presence of [γ‐32P]ATP or [γ‐32P]GTP. Replacement of arginine‐88 of adk with glycine resulted in the loss of enzymic activity. The purified protein also showed Ndk (nucleoside diphosphate kinase)‐like activity as it transferred terminal phosphate from [γ‐32P]ATP to all nucleoside diphosphates, converting them into corresponding triphosphates. However, Ndk‐like activity of Ak was not observed with [γ‐32P]GTP. Immunoblot analysis of various cellular fractions of M. tuberculosis H37Rv revealed that Ak is a cytoplasmic protein. The dual activity of Ak as both nucleoside mono‐ and di‐phosphate kinases suggested that this enzyme may have a role in RNA and DNA biosynthesis in addition to its role in intracellular nucleotide metabolism.
Optimization of submerged‐culture conditions for mycelial growth and exo‐biopolymer production by Auricularia polytricha (wood ears fungus) using the methods of uniform design and regression analysis
Authors: Xu Chun‐Ping , Yun Jong‐Won
Published: October 2003

This paper is concerned with the optimization of submerged culture conditions for mycelial growth and exo‐biopolymer production by Auricularia polytricha by one‐factor‐at‐a‐time and uniform design (UD) methods. First, the one‐factor‐at‐a‐time method was adopted to investigate the effects of environmental factors (i.e., initial pH and temperature) and variables of medium components (i.e., carbon, nitrogen and mineral sources) on mycelial growth and exo‐biopolymer production. Sucrose, yeast extract, and K2HPO4 were identified to be the most suitable carbon, nitrogen, and mineral sources, respectively. The optimal temperature and initial pH for mycelial growth and exo‐biopolymer production were found to be 25 °C and 5.0, respectively. Subsequently, the concentrations of sucrose, yeast extract, and K2HPO4 were optimized using the UD method. The optimal concentrations for the enhanced production were determined as 6% (w/v) sucrose, 2.5% (w/v) yeast extract, and 0.3% (w/v) K2HPO4 for mycelial yield, and 6% (w/v) sucrose, 1.28% (w/v) yeast extract, and 0.3% (w/v) K2HPO4 for exo‐biopolymer production, respectively. Subsequent experiments confirmed the validity of the models. This optimization strategy in shake‐flask culture led to a mycelial yield of 6.14 g/l, and exo‐biopolymer production of 2.12 g/l, respectively, which were considerably higher than those obtained in the preliminary studies. By using the optimized medium, the maximum concentrations of mycelial biomass and exo‐biopolymer in a 5 litre stirred‐tank bioreactor indicated 35.3 g/l and 3.1 g/l, respectively.
Maize (Zea mays)‐derived bovine trypsin: characterization of the first large‐scale, commercial protein product from transgenic plants
Authors: Woodard Susan L. , Mayor Jocelyne M. , Bailey Michele R. , Barker Donna K. , Love Robert T. , Lane Jeffrey R. , Delaney Donna E. , McComas‐Wagner Janet M. , Mallubhotla Hanuman D. , Hood Elizabeth E. , Dangott Lawrence J. , Tichy Shane E. , Howard John A.
Published: October 2003

Bovine trypsin (EC 3.4.21.4) is an enzyme that is widely used for commercial purposes to digest or process other proteins, including some therapeutic proteins. The biopharmaceutical industry is trying to eliminate animal‐derived proteins from manufacturing processes due to the possible contamination of these products by human pathogens. Recombinant trypsin has been produced in a number of systems, including cell culture, bacteria and yeast. To date, these expression systems have not produced trypsin on a scale sufficient to fulfill the need of biopharmaceutical manufacturers where kilogram quantities are often required. The present paper describes commercial‐level production of trypsin in transgenic maize (Zea mays) and its physical and functional characterization. This protease, the first enzyme to be produced on a large‐scale using transgenic plant technology, is functionally equivalent to native bovine pancreatic trypsin. The availability of this reagent should allow for the replacement of animal‐derived trypsin in the processing of pharmaceutical proteins.
Lipase‐catalysed transesterification of soya bean oil for biodiesel production during continuous batch operation
Authors: Du Wei , Xu Yuanyuan , Liu Dehua
Published: October 2003

The effects of temperature, oil/alcohol molar ratio and by‐product glycerol were studied during Lipozyme TL IM‐catalysed continuous batch operation when short‐chain alcohols were used as the acyl acceptor. In non‐continuous batch operation, the optimal oil/alcohol ratio and temperature were 1:4 and 40–50 °C; however, during the continuous batch operation, the optimal oil/alcohol ratio and temperature were 1:1 and 30 °C; 95% of enzymic activity remained after 10 batches when isopropanol was adopted to remove by‐product glycerol during repeated use of the lipase.
Temporal response pattern of biochemical analytes in experimental diabetes
Authors: Mori Daniela M. , Baviera Amanda M. , De Oliveira Ramalho Lizeti Toledo , Vendramini Regina C. , Brunetti Iguatemy L. , Pepato Maria T.
Published: October 2003

The activities of the enzymes aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), lactate dehydrogenase (LD), creatine kinase (CK), amylase (AMS) and angiotensin converting enzyme (ACE) have been used to assess the toxic effects of xenobiotics that have hypoglycaemic action in hepatic, pancreatic, renal and muscle tissue. Using a validated experimental model of diabetes mellitus in rats, we ascertained whether this syndrome itself affected the serum activities of these enzymes over a 53‐day period. Levels of hepatic enzymes AST, ALT and ALP were higher in the streptozotocin (STZ)‐diabetic rats (group D), but were controlled by insulin therapy (group DI). AMS was reduced in group D and unchanged in group DI rats. Proteinuria was detected 1 day after STZ administation and partially controlled by insulin (group DI); its early presence in group D rats, and the lack of any change in serum ACE in this group, indicates that proteinuria is the better marker for microangiopathy. Microscopic examination of liver, kidney, heart and skeletal muscles (soleus and extensor digitorum longus) revealed various alterations in group D rat tissues, which were less pronounced in group DI. The liver, pancreas and kidney tissue‐damage was consistent with the altered serum levels of AST, ALT, ALP and AMS and proteinuria. We conclude that: (i) rigorous control is required when these serum‐enzyme levels are used as indicators of tissue toxicity in experimental diabetes, and (ii) LD, CK and bilirubin serum levels, which are unaffected by diabetes, can be used when testing effects of xenobiotics on tissues.
l‐Tyrosine prevents aggregation of therapeutic proteins by γ‐irradiation
Authors: Assemand Emma , Lacroix Monique , Mateescu Mircea‐Alexandru
Published: October 2003

The present paper describes a protective role of l‐tyrosine against aggregation of caeruloplasmin and haemoglobin therapeutic proteins during their sterilization by γ‐irradiation in the aqueous phase. Irradiation of proteins, known to induce their degradation in the presence of oxygen, generates aggregation under oxygen‐free conditions. It was found that l‐tyrosine present during irradiation in deoxygenated media prevents protein aggregation even at high doses (10 kGy), as asserted by SDS/PAGE and high‐performance size‐exclusion chromatography. The protective role of l‐tyrosine, allowing the γ‐irradiation treatment of therapeutic proteins in solution without conformational alteration, is probably exerted by scavenging oxygen radicals produced by irradiation‐induced water radiolysis. It was also found that haemoglobin had a greater stability than caeruloplasmin under γ‐irradiation treatment.
Similarities between the thermal inactivation kinetics of Bacillus amyloliquefaciensα‐amylase in an aqueous solution of sodium dodecyl sulphate and the kinetics in the solution of anionic‐phospholipid vesicles
Authors: Tanaka Atsushi , Hoshino Eiichi
Published: October 2003

An anionic surfactant, SDS, is commonly used to model compounds of negatively charged phospholipids. The effect of SDS on the thermal inactivation of BAA (α‐amylase from Bacillus amyloliquefaciens) was compared with the effect of negatively charged phospholipid vesicles of DOPA (dioleoylphosphatidic acid) at 40–55 °C. The inactivation kinetics revealed that both SDS below its c.m.c. (critical micellar concentration) and DOPA vesicles accelerated the inactivation and the unfolding of the enzyme structure. Both SDS and DOPA vesicles lowered the activation enthalpy and entropy for the inactivation. The lowered activation parameters might be due to the relatively small energy requirement needed to reach the transition state from the ground state of BAA in the presence of the negatively charged hydrophobic environments. This study suggests an accelerated unfolding of BAA in the presence of SDS to be energetically similar to the accelerated unfolding in the presence of DOPA vesicles that involve a molten‐globule‐like state.
A reagentless nitric oxide biosensor based on haemoglobin/polyethyleneimine film
Authors: Liu Xinjian , Shang Libin , Pang Jiantao , Li Genxi
Published: October 2003

An unmediated NO biosensor was prepared by co‐immobilizing haemoglobin with polyethyleneimine at a pyrolytic graphite electrode surface. Haemoglobin exhibits direct electrochemistry in the membrane, and this modified electrode shows high stability and catalytic activity towards the reduction of NO. A linear relationship between the catalytic current and the concentration of NO was observed in the concentration ranges 1.0×10−7–8.0×10−6 M and 1.0×10−5–2.5×10−5 M, with a detection limit of 4.0×10−8 M.