bluuebunny/crossref_metadata_2025 huggingface dataset:
(In,Ga)As sidewall quantum wires on shallow-patterned InP (311)A
Authors: Zhou D. , Nötzel R. , Gong Q. , Offermans P. , Koenraad P. M. , van Veldhoven P. J. , van Otten F. W. M. , Eijkemans T. J. , Wolter J. H.
Published: March 2005

(In,Ga)As sidewall quantum wires (QWires) are realized by chemical beam epitaxy along [01-1] mesa stripes on shallow-patterned InP (311)A substrates. The QWires exhibit strong lateral carrier confinement due to larger thickness and In composition compared to the adjacent quantum wells, as determined by cross-sectional scanning-tunneling microscopy and microphotoluminescence (micro-PL) spectroscopy. The PL of the (In,Ga)As QWires with InP and quaternary (Ga,In)(As,P) barriers reveals narrow linewidth, high efficiency, and large lateral carrier confinement energies of 60–70meV. The QWires are stacked in growth direction with identical PL peak emission energy. The PL emission energy is not only controlled by the (In,Ga)As layer thickness but also by the patterned mesa height. Stacked (In,Ga)As QWires with quaternary barriers exhibit room temperature PL emission at 1.55μm in the technologically important wavelength region for telecommunication applications.
Vertical electronic coupling between InAs∕InP quantum-dot layers emitting in the near-infrared range
Authors: Miska P. , Even J. , Paranthoen C. , Dehaese O. , Jbeli A. , Senès M. , Marie X.
Published: March 2005

Stacked InAs quantum dots (QDs) grown on InP(113)B are analyzed both experimentally and theoretically in order to study the influence of the electronic vertical coupling between the QD layers. Improved growth conditions enable us to control the optimum QD height of the samples, thus yielding an emission wavelength of our nanostructures at about 1.55μm at room temperature. Three samples containing three QD layers with different vertical spacing are studied. The QD electronic structure is studied by continuous-wave photoluminescence and time-resolved photoluminescence experiments at low temperature. A simplified theoretical model is developed, yielding results consistent with experimental data. This analysis evidences the electronic coupling between the QD layers.
Two-prism setup for surface plasmon resonance studies
Authors: Mohanty Bhaskar Chandra , Kasiviswanathan S.
Published: March 2005

A two-prism experimental arrangement having wide angular scan ranges for the study of surface plasmon resonance is presented. The setup has a single rotating element instead of a high cost goniometer and a stationary photodetector which is positioned such that it always receives the reflected beam normally. The usefulness of the setup has been verified by experimental and theoretical studies of plasmon resonance at an Au–air interface.
Surface passivation using ultrathin AlNx film for Ge–metal–oxide–semiconductor devices with hafnium oxide gate dielectric
Authors: Gao Fei , Lee S. J. , Pan J. S. , Tang L. J. , Kwong Dim-Lee
Published: March 2005

A surface passivation method to improve the film quality of HfO2 gate dielectric on Ge substrate by using ultrathin AlNx layer is reported. Results show that the AlNx passivation layer is more effective in suppressing the GeOx formation at the HfO2∕Ge interface, resulting in improved C–V characteristics, than surface nitridation-passivated Ge devices. In addition, a thermal stability study shows AlNx passivation is promising for future Ge metal–oxide–semiconductor devices.
Neutron irradiation of MgB211: From the enhancement to the suppression of superconducting properties
Authors: Putti M. , Braccini V. , Ferdeghini C. , Gatti F. , Grasso G. , Manfrinetti P. , Marré D. , Palenzona A. , Pallecchi I. , Tarantini C. , Sheikin I. , Aebersold H. U. , Lehmann E.
Published: March 2005

In this letter, we present the effect of neutron irradiation up to fluences of 1.4×1020cm−2 on the superconducting properties of MgB2. In order to obtain a homogeneously distributed disorder, the experiment was carried out on bulk samples prepared with the B11 isotope. Up to fluences of 1018cm−2, the critical temperature (Tc) is slightly diminished (36K) and the superconducting properties are significantly improved; the upper critical field is increased from 13.5T to 20.3T at 12K and the irreversibility field is doubled at 5K. For the largest neutron fluence, Tc is suppressed down to 9.2K and the superconducting properties come out strongly degraded.
Substitution of H− for O− and H− emissions of 12CaO∙7Al2O3
Authors: Huang F. , Li J. , Xian H. , Tu J. , Sun J. Q. , Yu S. Q. , Li Q. X. , Torimoto Y. , Sadakata M.
Published: March 2005

By using an anion-exchanging method, about 90% of the O− anions in the C12A7-O− microporous crystal ([Ca24Al28O64]4+∙4O−) have been substituted primarily by the H− anions, leading to the successful formation of a new H− emission material, C12A7-H−([Ca24Al28O64]4+∙4H−). A sustainable and stable emission of H−, in a current density of μA∕cm2 level, has been obtained by supplying H2 and electrons on the backside of the C12A7-H− sample. The emission features of C12A7-H−, including temperature and field effects, have been investigated. It is expected that the present material could be practically used as an H− anion generator.
Impact of oxygen ambient on ferroelectric properties of polar-axis-oriented CaBi4Ti4O15 films
Authors: Kato Kazumi , Tanaka Kiyotaka , Suzuki Kazuyuki , Kimura Tatsuo , Nishizawa Kaori , Miki Takeshi
Published: March 2005

Polar-axis oriented CaBi4Ti4O15(CBTi144) films were fabricated on Pt foils using a complex metal alkoxide solution. The oxygen ambient during crystallization of the films impacted the crystal perfection, crystallite size, and the ferroelectric properties. The 500mm thick film crystallized in oxygen flow had single columnar structure and in-plane grain size of about 200nm. The Scherrer’s crystallite diameter was calculated as about 110nm. The ferroelectric properties were improved. The Pr and Ec of the film enhanced as 33.6μC∕cm2 and 357kV∕cm, respectively, at an applied voltage of 50V. Voltage applied for full polarization switching was lowered by controlling oxygen stoichiometry of the film. Indeed, the polar-axis-oriented CBTi144 films would open up possibilities for devices as Pb-free ferroelectric materials.
Compressibility of Nb2AsC to 41 GPa
Authors: Kumar Ravhi S. , Rekhi Sandeep , Cornelius A. L. , Barsoum Michel W.
Published: March 2005

Room temperature synchrotron x-ray diffraction experiments were performed on the layered hexagonal ternary carbide Nb2AsC in a diamond anvil cell to a pressure of 41 GPa. The structure is stable with no phase transitions observed in this pressure range. The bulk modulus is 224±2GPa, with a pressure derivative of 4; the former is the highest bulk modulus for a Mn+1AXn (MAX) phase, including Ti3SiC2, measured to date. Nb2AsC is also the first MAX phase for which the compressibility along the a direction is higher than along the c direction; in other words, the c∕a ratio increases strongly with applied pressure.
The central and basolateral nuclei of the amygdala exhibit opposite diurnal rhythms of expression of the clock protein Period2
Authors: Lamont Elaine Waddington , Robinson Barry , Stewart Jane , Amir Shimon
Published: March 2005

There is considerable evidence that circadian rhythms in mammals can be modulated by emotional state, but how emotional state modulates specific circadian outputs is poorly understood. We analyzed the expression of the circadian clock protein Period2 (PER2) in three regions of the limbic forebrain known to play key roles in emotional regulation, the central nucleus of the amygdala (CEA), the basolateral amygdala (BLA), and the dentate gyrus (DG). We report here that cells in all three regions exhibit daily rhythms in expression of PER2 that are under the control of the master clock, the suprachiasmatic nucleus (SCN). The rhythm in the CEA and the rhythms in the BLA and DG are diametrically opposite in phase and are differentially affected by adrenalectomy. Adrenalectomy completely abolished the PER2 rhythm in the CEA but had no effect on the PER2 rhythms in the BLA and DG. We previously reported a rhythm in PER2 expression in the oval nucleus of the bed nucleus of the stria terminalis that is identical in phase and sensitivity to adrenalectomy to that found in the CEA. Together, these findings show that key structures of the limbic forebrain exhibit daily oscillations in clock gene expression that are controlled not only by input from the SCN but, importantly, by hormonal and neurochemical changes that normally accompany motivational and emotional states. Thus, cells within these areas are strategically positioned to integrate the inputs from the SCN and emotional states to modulate circadian rhythms downstream from the SCN clock.
Fleshy fruits – origins, niche shifts, and diversification
Authors: Bolmgren Kjell , Eriksson Ove
Published: March 2005

We examined shifts in fruit type, fleshy vs non‐fleshy, in relation to habitat‐related niche shifts, species richness, and historical distribution, in 50 phylogenetically independent plant lineages. Each lineage consisted of a sister‐group pair of fleshy vs non‐fleshy taxa and their outgroup. Niche shifts were assessed based on plant community characteristics. Two niche dimensions assumed to reflect community dynamics were derived: spatial predictability of disturbances and canopy closure. Phylogenetically independent origins of fleshy fruit types (1) were correlated with changes to habitats characterized by more shaded and spatially more unpredictable disturbances, (2) had an opposite effect on species richness in woody and herbaceous clades, enhancing species richness in woody clades, and (3) were continuously distributed over a period covering the last 70 million years. These results support the hypothesis that fleshy fruit evolution is driven by vegetation dynamics, and suggest that the strength of frugivore mediated selection on fleshy fruits increases when recruitment sites are spatially unpredictable and/or characterized by low light conditions.
Negative indirect effects of an avian insectivore on the fruit set of an insect‐pollinated herb
Authors: Meehan T. D. , Lease H. M. , Wolf B. O.
Published: March 2005

Though an abundance of research has focused on direct interactions between birds and plants, relatively few studies have reported on indirect interactions. Of those reports, all have focused on positive indirect effects of birds on plants through predation of plant natural enemies. We conducted an observational study along the Middle Rio Grande in New Mexico to determine if avian aerial insectivores had a negative, indirect impact on insect‐pollinated plants through predation of insect pollinators. We found considerable taxonomic overlap, at the order and family level, between insects visiting sweet clover (Melilotus officinalis) and those eaten by cliff swallows (Hirundo pyrrhonota). We found a significant negative relationship between proximity of sweet clover to cliff swallow breeding colonies and sweet clover fruit set during the cliff swallow nestling period. The apparent effect of cliff swallows was strongest within 200 m of breeding colonies (approximately 50% reduction in fruit set) and decreased nonlinearly to a distance of approximately 400 m. Finally, we found that the clover fruit set gradient disappeared after the nestling period, when chicks had fledged and the colony was abandoned.
On the roles of time, space and habitat in a boreal small mammal assemblage: predictably stochastic assembly
Authors: Morris Douglas W.
Published: March 2005

Ecologists continue to debate the roles of deterministic versus stochastic (or neutral) processes in the assembly of ecological communities. The debate often hinges on issues of temporal and spatial scale. Resolution of the competing views depends on a detailed understanding of variation in the structure of local communities through time and space. Analyses of twelve years of data on a diverse assemblage of 13 boreal small mammal species revealed both deterministic and stochastic patterns. Stochastic membership in the overall community created unique assemblages of species in both time and space. But the relative abundances of the two codominant species were much less variable, and suggest a significant role for strong interactions that create temporal and spatial autocorrelation in abundance. As species wax and wane in abundance, they are nevertheless subject to probabilistic rules on local assembly. At the scales I report on here, poorly understood large scale processes influence the presence and absence of the majority of (sparse) species in the assembly. But the overall pool of species nevertheless obeys local rules on their ultimate stochastic assembly into groups of interacting species.
Infection with cowpox virus decreases female maturation rates in wild populations of woodland rodents
Authors: Telfer Sandra , Bennett Malcolm , Bown Kevin , Carslake David , Cavanagh Rachel , Hazel Sarah , Jones Trevor , Begon Michael
Published: March 2005

Sublethal effects of parasitic infection, such as reductions in reproductive rate, can significantly affect host population dynamics. Here we show that in wild populations of bothClethrionomys glareolus(bank vole) andApodemus sylvaticus(wood mouse), females infected with cowpox virus are likely to delay maturation and therefore reproduction – in most cases until the following breeding season. Some infected bank voles do mature in their year of birth but still take longer than uninfected females. Together with our previous demonstration that individuals infected with cowpox virus in the summer survive better than uninfected individuals, these results support the prediction that hosts that develop an acute infection may best optimise their fitness by decreasing current reproduction to maximise the probability of surviving infection. Moreover, as the proportion of individuals infected increases with density, the reduction in host fecundity may have significant consequences for host dynamics.
Dynamics of populations on the verge of extinction
Authors: Oborny, Géza Meszéna and György Szabó Beáta
Published: March 2005

Theoretical considerations suggest that extinction in dispersal‐limited populations is necessarily a threshold‐like process that is analogous to a critical phase transition in physics. We use this analogy to find robust, common features in the dynamics of extinctions, and suggest early warning signals which may indicate that a population is endangered. As the critical threshold of extinction is approached, the population spontaneously fragments into discrete subpopulations and, consequently, density regulation fails. The population size declines and its spatial variance diverges according to scaling laws. Therefore, we can make robust predictions exactly in the range where prognosis is vital, on the verge of extinction.
Distribution of phlebotomine sandflies, of the subgenus Larroussius, in Morocco
Authors: Guernaoui S. , Pesson B. , Boumezzough A. , Pichon G.
Published: March 2005

Abstract.  Adult sandflies (Diptera: Psychodidae) of the genus Phlebotomus and of the subgenus Larroussius were collected with sticky traps from thirty‐four localities in central and south‐western Morocco. Four Larroussius species were present in this area, Phlebotomus perniciosus Newstead, being the most widespread and abundant species particularly in the mountainous area, was sympatric with the closely related species Phlebotomus longicuspis Nitzulescu. Only one male of P. perniciosus displayed the bifid copulatory valves characteristic of the species. All specimens showed copulatory valves curved at their apex. The number of coxite hairs is a taxonomical tool that differentiates this morph of P. perniciosus from P. longicuspis. Phlebotomus ariasi Tonnoir was collected from six mountainous stations. Phlebotomus mariae Rioux et al. was scarce; only five males were collected and were often associated with P. ariasi.
In vitro rearing of the screwworm fly Wohlfahrtia magnifica
Authors: Farkas R. , Hell É. , Hall M. J. R. , Gyurkovszky M.
Published: March 2005

Abstract.  Wohlfahrtia magnifica (Schiner) (Diptera: Sarcophagidae) is the main agent of traumatic myiasis in many European, African and Asian countries. Although it can be reared in vivo without technical difficulty, such rearing presents ethical problems. Studies were therefore made of in vitro rearing to facilitate development of laboratory colonies that could be used in a wide range of biological, physiological and applied studies of W. magnifica, particularly in the long period of the year when natural populations of the fly are unavailable for study. Parental colonies of W. magnifica were established from larvae collected from natural infestations of sheep and cattle in central Hungary. First stage larvae were harvested from gravid females and were reared in groups of 5–20 on one of six artificial diets. The diets were based on various combinations of five to seven of eight ingredients: water, agar, blood (heparinized or dried), ground meat, egg yolk, low‐fat milk powder, yeast and 10% formol. The larvae were incubated on the diets at 37°C. There was no mortality of first stage larvae, which appeared to feed together in foci, in a natural manner. However, during the second stage, and especially after renewal of diet associated with disturbance of the larvae, many larvae began to disperse, crawling over the surface of the media and feeding less intensively. Mortality of larvae during all larval stadia was 64–98%, compared to 33% in batches of third stage larvae collected from natural infestations. The mean weights of puparia from artificial diets ranged from 38.7 to 59.3 mg, compared to 92.2 mg of puparia from larvae collected from natural infestations. There was a high mortality in the pupal stage, from 61 to 100%. Only a maximum of 6% of first stage larvae were successfully reared to the adult stage. Further studies are needed to identify factors present or absent in the diets that contributed to the present poor development of W. magnifica in vitro.
Malaria transmission dynamics in central Côte d'Ivoire: the influence of changing patterns of irrigated rice agriculture
Authors: Koudou B. G. , Tano Y. , Doumbia M. , Nsanzabana C. , Cissé G. , Girardin O. , Dao D. , N'Goran E. K. , Vounatsou P. , Bordmann G. , Keiser J. , Tanner M. , Utzinger J.
Published: March 2005

Abstract.  The dynamics of malaria transmission was studied comparatively in the villages of Zatta and Tiémélékro, central Côte d'Ivoire, from February 2002 to August 2003. Prominent agroecosystems in these villages are irrigated rice growing and vegetable farming, respectively. Mosquitoes (Diptera: Culicidae) were collected on human bait at night and by pyrethrum knock‐down spray sheet collections at four randomly selected sentinel sites in each village. In 2002, for a total of 96 man‐nights per village, 7716 mosquitoes were collected in Zatta and 3308 in Tiémélékro. In 2003, with half the sampling effort, 859 and 2056 mosquitoes were collected in Zatta and Tiémélékro, respectively. Anopheles gambiae Giles s.l. was the predominant mosquito and the key malaria vector throughout, followed by An. funestus Giles. Anthropophily among adult female Anopheles exceeded 95% in both villages. Comparison between years revealed that the biting rate of An. gambiae s.l. in Zatta decreased several‐fold from 49.3 bites per person per night (b/p/n) in 2002 to 7.9 b/p/n in 2003 (likelihood ratio test (LRT) = 1072.66; P < 0.001). Although the biting rate remained fairly constant in Tiémélékro, the difference between years was significant (16.1 vs. 18.2 b/p/n; LRT = 148.06; P < 0.001). These observations were paralleled by a marked decrease in the infective rate of An. gambiae s.l. in Zatta (4.6–1.2%), and an increase in Tiémélékro (3.1–7.6%). Meanwhile, the entomological inoculation rate of An. gambiae s.l. decreased 21‐fold in Zatta, from 789 to 38 infective bites per person per year (ib/p/y), whereas it remained high in Tiémélékro (233 vs. 342 ib/p/y). The interruption of irrigated rice growing in Zatta in 2003, consequential to a farmers' conflict over land, might be the underlying cause for the significant reduction in malaria transmission, whereas more stable conditions occurred in Tiémélékro.
North American face flies Old World origins: mitochondrial evidence
Authors: Cummings M. A. , Moon R. D. , Krafsur E. S.
Published: March 2005

Abstract.  Analysis of a 513 base sequence of mitochondrial cytochrome oxidase I gene in Musca autumnalis De Geer (Diptera: Muscidae) from the U.S.A., England, Russia and Kazakhstan confirms that North American flies originated in Western Europe. Flies from the U.S.A., England and southern Russia shared most of their mitochondrial diversities, but face flies from Kazakhstan were substantially dissimilar, suggesting highly restricted gene flow and a species complex within the Palearctic.
Sand fly species of Sanlıurfa province in Turkey
Authors: Toprak S. , Ozer N.
Published: March 2005

Abstract.  The species composition and seasonal abundance of sand flies (Diptera: Phlebotominae) were studied in the years 2000–2002 in the Sanlıurfa region, which is the largest focus of cutaneous leishmaniasis in south‐eastern Turkey. Sixteen species were identified among 29 771 specimens collected at 17 different sites by light traps, sticky papers and aspirators. The most common species were Phlebotomus papatasi (Scopoli) (45.4%), P. perfiliewi Parrot (21.9%), and P. sergenti Parrot (19.4%). The other species found were P. major Adler & Theodor (3%), P. neglectus Leger & Pesson (2.2%), P. brevis Theodor & Mesghali (2%), P. alexandri Sinton (1.9%), P. galilaeus Theodor (1.6%), P. halepensis Theodor (0.84%), Sergentomyia adleri Theodor (0.78%), S. dentata Sinton (0.49%), S. minuta Rondani (0.42%), S. theodori Parrot (0.16%), P. kazeruni Theodor & Mesghali (0.001%) and P. mascitti Grassi (0.001%) and one unidentified Phlebotomus species. Among these species P. galilaeus, S. minuta and S. dentata are the first records for this area. All species showed seasonal fluctuations, with the period of highest abundance between May and October.
Borreliacidal activity of saliva of the tick Amblyomma americanum
Authors: Ledin K. E. , Zeidner N. S. , Ribeiro J. M. C. , Biggerstaff B. J. , Dolan M. C. , Dietrich G. , VredEvoe L. , Piesman J.
Published: March 2005

Abstract.  Amblyomma americanum (Linneaus) (Acari: Ixodidae), an important tick vector of human and animal disease, is not a competent vector of the bacterial agent of Lyme disease, Borrelia burgdorferi, although its range overlaps the geographical distribution of Lyme disease within the United States. A possible mechanism that could prevent acquisition of B. burgdorferi spirochetes from infected hosts is the toxic effect of A. americanum saliva on B. burgdorferi. The data presented here indicate that after 24 and 48 h of exposure to A. americanum saliva, significantly fewer B. burgdorferi were alive compared to treatment controls as assessed by spirochete motility under dark‐field microscopy and resistance to the dead stain, propidium iodide. After 48 h, fewer than 13% of saliva‐exposed B. burgdorferi were alive. In contrast, significantly more B. burgdorferi exposed to Ixodes scapularis (Acari: Ixodidae) saliva survived after 24 or 48 h compared to A. americanum saliva or treatment controls.
Filarial susceptibility and effects ofWolbachiainAedes pseudoscutellarismosquitoes
Authors: Dutton T. J. , Sinkins S. P.
Published: March 2005

Abstract. The mosquitoAedes pseudoscutellaris(Theobald), a member of theAedes(Stegomyia)scutellariscomplex (Diptera: Culicidae), is an important vector of subperiodicWuchereria bancrofti(Cobbold) (Spirurida: Onchocercidae), causing human lymphatic filariasis, on South Pacific islands. Maternal inheritance of filarial susceptibility in the complex has previously been asserted, and larval tetracycline treatment reduced susceptibility; the maternally inheritedWolbachiain these mosquitoes were suggested to be responsible. To investigate the relationship of these two factors, we eliminatedWolbachiafrom a strain ofAe. pseudoscutellarisby tetracycline treatment, and tested filarial susceptibility of the adult female mosquitoes usingBrugia pahangi(Edeson & Buckley). Filarial susceptibility was not significantly different inWolbachia‐free and infected lines ofAe. pseudoscutellaris, suggesting that theWolbachiain these mosquitoes do not influence vector competence. Crosses betweenWolbachia‐infected males and uninfected females ofAe. pseudoscutellarisshowed cytoplasmic incompatibility (CI), i.e. no eggs hatched, unaffected by larval crowding or restricted nutrient availability, whereas these factors are known to affect CI inDrosophila simulans. Reciprocal crosses betweenAe. pseudoscutellaris and Ae. katherinensisWoodhill produced no progeny, even when both parents wereWolbachia‐free, suggesting that nuclear factors are responsible for this interspecific sterility.
Repellency of deet and SS220 applied to skin involves olfactory sensing by two species of ticks
Authors: Carroll J. F. , Klun J. A. , Debboun M.
Published: March 2005

Abstract.  Responses of host‐seeking nymphs of the blacklegged tick, Ixodes scapularis Say and lone star tick, Amblyomma americanum (Linnaeus) (Acari: Ixodidae) to the repellents N,N‐diethyl‐3‐methylbenzamide (deet) and (1S, 2′S)‐2‐methylpiperidinyl‐3‐cyclohexene‐1‐carboxamide (SS220) were studied using fingertip laboratory bioassays. Ethanol solutions of both compounds applied to the skin strongly repelled both species of ticks at 0.8 and 1.6 µmole of compound/cm2 skin. The ticks were also repelled when two layers of organdie cloth covered the portion of a finger treated with either deet or SS220. Gas chromatographic analyses of the outer layer of cloth that had covered skin treated with 1.6 µmole compound/cm2 skin revealed only 0.1 nmole SS220/cm2 cloth and 2.8 nmole deet/cm2 cloth. However, in bioassays in which a single layer of cloth was treated with a dose of deet or SS220 equivalent to the amount found in the outer layer of cloth, ticks were not repelled. Results unequivocally demonstrated that these ticks responded to the repellents in the vapour phase when repellent treated skin was covered with cloth to obviate tactile contact with them, and made it clear that the ticks detect the repellents by olfactory sensing. Heretofore, the mode of action of deet and SS220 was unclear.
Short‐term distribution of 134Cs in relation to 51Cr‐EDTA after intravenous dose in goats
Authors: Kaikkonen M. , De Gritz B. , Eriksson L.
Published: March 2005

Aim:  The aim of this study was to gather information about the short‐term rate of caesium uptake (incorporation) in different animal tissues and explain them with known physiological mechanisms affecting ion distribution.

Methods:  Six goats were given an intravenous bolus containing 134Cs as a tracer and 51Cr‐EDTA as an extracellular marker. After 30 min, the animals were killed and the activity concentration of radioactive isotopes in different tissues and fluid compartments were measured.

Results:  The highest relative activity concentration of 134Cs was found in kidney cortex, with a tissue/plasma‐ratio around 50. In urine, the ratio varied between 5 and 28. In the salivary gland, cardiac muscle and small intestine the ratio was around 11, 7 and 6, respectively. The contents of small intestine had an average activity concentration five times that of plasma. In skeletal muscle the terminal activity concentration was surprisingly low, with a tissue/plasma ratio mostly far less than unity. Even in connective tissue and cartilage the terminal activity concentration was generally higher than in skeletal muscle.

Conclusion:  The rate of uptake of caesium varies widely from tissue to tissue. Many of these differences can be explained with differences in Na,K‐ATPase activity. Also, perfusion and accessibility play a role in some tissues, like brain and possibly part of the skeletal muscles. The short‐term distribution of caesium differs distinctly from the long‐term distribution reported in literature.
The Salmonella genomic island 1 is an integrative mobilizable element
Authors: Doublet Benoît , Boyd David , Mulvey Michael R. , Cloeckaert Axel
Published: March 2005

Salmonella genomic island 1 (SGI1) is a genomic island containing an antibiotic resistance gene cluster identified in several Salmonella enterica serovars. The SGI1 antibiotic resistance gene cluster, which is a complex class 1 integron, confers the common multidrug resistance phenotype of epidemic S. enterica Typhimurium DT104. The SGI1 occurrence in S. enterica serovars Typhimurium, Agona, Paratyphi B, Albany, Meleagridis and Newport indicates the horizontal transfer potential of SGI1. Here, we report that SGI1 could be conjugally transferred from S. enterica donor strains to non‐SGI1 S. enterica and Escherichia coli recipient strains where it integrated into the recipient chromosome in a site‐specific manner. First, an extrachromosomal circular form of SGI1 was identified by PCR which forms through a specific recombination of the left and right ends of the integrated SGI1. Chromosomal excision of SGI1 was found to require SGI1‐encoded integrase which presents similarities to the lambdoid integrase family. Second, the conjugal transfer of SGI1 required the presence of a helper plasmid. The conjugative IncC plasmid R55 could thus mobilize in trans SGI1 which was transferred from the donor to the recipient strains. By this way, the conjugal transfer of SGI1 occurred at a frequency of 10−5−10−6 transconjugants per donor. No transconjugants could be obtained for the SGI1 donor lacking the int integrase gene. Third, chromosomal integration of SGI1 occurred via a site‐specific recombination between a 18 bp sequence found in the circular form of SGI1 and a similar 18 bp sequence at the 3′ end of thdF gene in the S. enterica and E. coli chromosome. SGI1 appeared to be transmissible only in the presence of additional conjugative functions provided in trans. SGI1 can thus be classified within the group of integrative mobilizable elements (IMEs).
Mechanism and Specificity of l‐ and d‐6‐Hydroxynicotine Oxidase
Authors: Decker K. , Dai V. D.
Published: March 2005

l‐6‐Hydroxynicotine oxidase, a FAD‐protein, coverts in the presence of oxygen l‐6‐hydroxynicotine to [6‐hydroxypyridyl(3)]‐(γ‐N‐methylaminopropyl)‐ketone; the overall process, whose stoichiometry has been established, consists of the enzyme‐catalyzed dehydrogenation of the substrate followed by spontaneous hydrolysis of the intermediate enamine. Titration of the enzyme anaerobically with substrate or dithionite spectrally does not indicate formation of a semiquinoid flavin, while upon irradiation in the presence of ethylenediaminetetraacetate, spectral changes take place which seem to relflect the existence of a transient radical stage. Molecular oxygen functions as electron acceptor in the oxidase reaction, other artificial or natural redox systems being inactive or even, as methylene blue, inhibitory to the l‐6‐hydroxynicotine oxidation. Previous evidence for the almost absolute structural and stereochemical specificity of both l‐and d‐6‐hydroxynicotine oxidases was extended.
Ligand‐Protein Interactions in Imidazole and 1,2,4‐Triazole Complexes of Methaemoglobin from Chironomus plumosus
Authors: Mohr P. , Scheler W. , Schumann H. , Müller K.
Published: March 2005

Imidazole, 4(5)‐methylimidazole, N‐methylimidazole, N‐vinylimidazole, 1,2,4‐triazole, 3‐amino‐1,2,4‐triazole and N‐methyl‐1,2,4‐triazole interact with methaemoglobin from Chironomus plumosus. In a weakly acidic environment all complexes show light absorption spectra of the parahaematin type with maxima near 535 and 415 mμ.

The affinity of these ligands to Chironomus‐methaemoglobin rises with increasing basic strength, with the exception of 3‐amino‐1,2,4‐triazole.

The spectra of the N‐alkylated imidazole‐ or triazole‐complexes are pH‐invariant, while those of the complexes with ligands containing a free NH‐group shift their maxima to longer wavelengths in alkaline medium (about 542 and 417 mμ).

This spectral change is attributed to the deprotonation of the NH‐group of the bound ligands. The ionization constants of this reaction have been estimated. They demostrate a strong increase of the acidity of these ligands as a result of their interaction with the haemoprotein.

Furthermore, the ligands influence the ionization constants of some haemin‐linked protein groups.

The results are an example of the changes of the electronic properties of low‐molecular compounds (drugs etc.) interacting with specific receptors of biomacromolecules and vice versa.
Significance of Ribonucleotide Reduction in the Biosynthesis of Deoxyribonucleotides in Escherichia coli
Authors: Karlström O. , Larsson A.
Published: March 2005

A pyrimidine auxotroph of Escherichia coli, possessing decreased deaminase activities for cytidine and deoxycytidine, was grown with uniformly 14C‐labeled cytidine or uridine as sole pyrimidine source. The incorporation of radioactivity into the individual mononucleotides of DNA and RNA was determined. The pyrimidine nucleotides were degraded, and the distribution of isotope between their pentose and base moieties was analyzed.

[14C]‐Cytidine was incorporated into RNA without loss of its isotope content. Furthermore, CMP of RNA and deoxyCMP of DNA had identical specific activities and pentose: base ratios. Therefore deoxyCMP of DNA was formed exclusively by reduction of a cytidine derivative.

Only approximately 20% of the pentose isotope content of [14C]‐uridine was retained after incorporation into RNA. CMP, UMP, deoxyCMP, and deoxyTMP isolated from the nucleic acids had approximately equal specific activities and pentose: base ratios, indicating that both pyrimidine deoxyribonucleotides were formed by ribonucleotide reduction.

[14C]‐Cytidine was converted to UMP of RNA with almost complete loss of isotope from the ribosyl moiety, but was converted to deoxyTMP of DNA with little loss of label. After estimation of different enzymatic activities in cell‐free extracts it was concluded that the major pathway yielding deoxyTMP of DNA did not involve deoxyTMP synthetase but rather proceeded directly from a deoxycytidine compound.
Initiation of DNA‐Dependent RNA Synthesis and the Effect of Heparin on RNA Polymerase
Authors: Walter G. , Zillig W. , Palm P. , Fuchs E.
Published: March 2005

The kinetics of RNA synthesis, catalyzed by DNA‐dependent RNA polymerase from Escherichia coli, show a lag phase at high ionic strength or at low temperature when using a double‐stranded DNA as template. This lag phase increases with decreasing temperature at constant ionic strength or with increasing ionic strength at constant temperature. With single‐stranded DNA as template, no lag phase is observed. The length of the lag phase is greatly shortened by pre‐incubation of the enzyme with DNA at low Mg++ concentration, independent of the presence of substrate.

Heparin is a strong inhibitor of free and DNA‐bound polymerase. Two heparin molecules are required for the inactivation of one enzyme molecule. Enzyme engaged in RNA synthesis is instantly inhibited on single‐stranded DNA but not on double‐stranded DNA. With the aid of this inhibitor it is shown that 10 minutes after the start of incubation, at 16°, all enzyme molecules have initiated RNA chains on double‐stranded DNA.
The Optical Activity of Urobilins Derived from Phycoerythrobilin
Authors: Cole W. J. , HEocha C. Ó , Moscowitz A. , Krueger W. R.
Published: March 2005

Phycoerythrobilin, one of two tetrapyrrolic prosthetic groups in R‐phycoerythrin, was the source of two crystalline urobilinoid pigments. One (catalytic urobilin peb) was prepared from phycoerythrobilin by hydrogenation followed by partial reoxidation of the resulting chromogen, and the other (isomeric urobilin peb) by prototropic isomerisation of phycoerythrobilin while still attached to protein. Both resembled d‐urobilin in possessing high dextrorotatory optical activity in chloroform solution and it is concluded that phycoerythrobilin contains one assymetric centre which has the same absolute configuration as the two centres shown previously in d‐urobilin. Isomeric urobilin peb must be formed under the influence of a stereospecific‐directing influence which leads to its containing two assymetric centres having the same absolute configuration as those in d‐urobilin. The optical activity of both urobilins from phycoerythrobilin was greatly reduced by methanol and trifluoroacetic acid, suggesting that in non‐polar solvents they are internally hydrogen bonded.
Thermodynamique des associations de poly A et poly U en milieu neutre et alcalin
Authors: Massoulié J.
Published: March 2005

The complexes of poly A and poly U are interesting models for studying the structure of nucleic acids. In the first part of this paper, the thermal stability of these complexes has been studied as a function of both pH and ionic strength in alkaline solution. The thermal stability is measured by the half transition temperatures, or Tm's. There are four different kinds of transitions: Tm2–1 refers to the dissociation of the two‐stranded complex, poly (A + U); Tm2–1 to the dissociation of the three‐stranded complex, poly (A + 2U) [4]. Tm2–2 is the temperature of half dissociation of poly (A + 2U) into poly (A + U) [1], and Tm2–2 is the temperature of rearrangement of 2 poly (A + U) into poly (A + 2U) [3] (Fig. 1). It is found that Tm2–1, and Tm3–1 decrease as pH increases above neutrality (Fig.2 and 3), but that Tm2–2 does not vary (Fig.3). This effect is readily explained if it is assumed that the ionisation of uracil brings a change in the state of the free poly U, but that the complexes themselves are not modified.

In the second part of the paper a simple thermodynamic formulation is given which represents satisfactorily the relationship between the four equilibria, as observed at neutral pH (Fig.1). A more complex treatment is then presented. It includes quantitation of electrostatic interactions, according to the theory of Kotin [18] and of the free enthalpy term corresponding to the organisation (stacking) of poly A. This leads to an excellent representation of the experimental data (Fig.5).

In alkaline solution, one can calculate the free enthalpy change associated with the ionisation of poly U at the Tm. According to our observations, it is likely that this is the only factor responsible for the decrease of Tm. Therefore, we can write that the sum of the free enthalpy of complex formation in the same conditions, but at pH 7, and of the free enthalpy of ionisation is zero. This leads to a determination of ΔG both as a function of temperature and ionic strength: the variation of ΔG with these factors is shown to be in good agreement with our detailed model. However, the absolute values are different, probably because of uncertainties concerning the data for poly A stacking enthalpy and entropy.

Apart from providing evaluation of the thermodynamic parameters for double and triple helix formation, our results lead us to emphasize the importance of the thermodynamic state of the unassociated polynucleotides. This may be particularly relevant when one considers the partially complementary secondary structures of RNA's.
On the Structure and Function of Reduced Nicotinamide Adenine Dinucleotide Phosphate‐Cytochrome f Reductase of Spinach Chloroplasts
Authors: Forti G. , Sturani E.
Published: March 2005

NADPH‐eytochrome f reductase from spinach chloroplasts has been purified, and its amino acid composition is reported.

The specificity of the enzyme for different electron acceptors has been studied. In addition to higher plant cytochrome f, Euglena gracilis cytochrome f and plastocyanin are reduced. The reaction with these acceptors occurs through a two‐step mechanism, whereas higher plant cytochrome f forms a ternary complex with NADPH and the enzyme. The Km values for NADPH in the reactions with the different electron acceptors, the Km's for the electron acceptors and the turnover numbers are reported.

The sulphydryl reagents slowly inactivate the enzyme and enhance the fluorescence of enzyme‐bound FAD and of the tryptophan residues of the protein. In the presence of NADPH, the inactivation is very rapid, and FADH2 is split from the apoenzyme. Preincubation of the enzyme with NADPH inactivates reversibly all the reactions except cytochrome f reductase.

The results are interpreted in terms of structure to function relationships and the significance of the NADPH‐cytochrome f reductase in photosynthetic electron transport is also discussed.
Préparation et propriétés de dérivés poly‐DL‐alanylés d'un inhibiteur de la trypsine (inhibiteur de Kunitz et Northrop)
Authors: Acher R. , Chauvet J. , Arnon R. , Sela M.
Published: March 2005

The basic trypsin inhibitor of bovine pancreas (Kunitz and Northrop inhibitor) has been alaninated with N‐carboxy‐DL‐alanine anhydride in a 0.05 M phosphate buffer, pH 7, containing 20% (v/v) dioxane.

When the molar ratio anhydride/inhibitor is 10 and the reaction is performed during 1 hour, approximately 70% of the α‐amino group are blocked but the four ∈‐amino groups are only weakly affected. The derivative has an inhibiting capacity similar to that of the native inhibitor. The performic acid oxidized product is subjected to tryptic hydrolysis and the peptides are separted by the fingerprinting technique, then analyzed. The detected peptides are simolar to those given by the oxidized inhibitor execept for the N‐terminal fragment which has about 2 additional alanine residues presumably on the α‐amino group.

When the molar ratio anhydride/inhibititor is 250 and the reaction is performed during 74 hours, the five amino groups are fully blocked. The derivative is virtually inactive. The oxidized product, split by trypsin, gives a peptide map from which the lysyl peptides are absent. In contrast junction peptides can be detected and analyzed. The average number of alanine residues fixed on each lysine has been determined. The four lysines react with N‐carboxy‐DL‐alanine anhydride in a similar manner. When the four lysines of the inhibitor are converted to homoarginine residues by guanidination, the activity remains, but when polyalanine chains (5–10 residues) are attached to these lysines, the activity is virtually lost. The results suggest that one or several ∈‐amino groups are involved in the interaction between inhibitor and trypsin.
Incorporation spécifique de la L‐[U‐14C] isoleucine dans le groupement hydroxy‐2 méthyl‐2 butyroyle de la glaucarubinone
Authors: Moron J. , Polonsky J.
Published: March 2005

2‐Hydroxy‐2‐methylbutyric acid (III) occurs esterified to glaucarubolone (II) in glaucarubinone (I), the bitter principle of Simaruba glauca (Simarubaceae).

No experimental results concerning the biosynthesis of this acid have yet been reported.

The biogenetic precursor of 2‐hydroxy‐2‐methylbutyric acid might be either mevalonic acid, acetoacetate, or isoleucine.

We have shown previously that mevalonic acid is not incorporated into the 2‐hydroxy‐2‐methylbutyrate component of glaucarubinone (I) although it is into glaucarubolone (II).

We now report our feeding experiments with two batches of young shoots of Simaruba glauca using l‐[U‐14C]isoleucine and sodium [1‐14C]acetate.

After 8 days the bitter principles were isolated and the total incorporation of radioactivity determined. The radioactive glaucarubinone (I) was hydrolysed to glaucarubolone (II) and 2‐hydroxy 2‐methyl butyric acid (III). This acid, when obtained from glaucarubolone after incorporation of acetate, has been found to be weakly labelled. In contrast, it carries essentially all the activity of glaucarubinone, when isolated after incorporation of isoleucine.

These results establish the specific incorporation of isoleucine into the 2‐hydroxy 2‐methyl butyroyl part of glaucarubinone.
The Regulation of Isoleucine‐Valine Biosynthesis in Saccharomyces cerevisiae
Authors: de Robichon‐Szulmajster H. , Magee P. T.
Published: March 2005

A study of threonine deaminase from Saccharomyces cerevisiae has been undertaken. The enzyme has been purified 50‐fold, with a low resolution of pyridoxal phosphate coenzyme. The purified enzyme is very unstable under all conditions tried so far. Properties have been studied with crude extracts. Optimum pH has been found to be 8.2. Isoleucine has complex effects on the enzyme activity. At a concentration of 0.1 mM, it is able to stimulate the enzyme. At higher concentrations, isoleucine inhibits. The Ki values increase with increasing pH, but 100% inhibition can be reached at all ranges of pH studied. Affinity of the enzyme for its substrate is even more strongly modified by pH.

a) Substrate cooperativity, nil at pH 7, intermediate at pH 8, seems to be maximum at pH 9. At any pH, the substrate cooperativity can be suppressed by addition of L‐valine. In addition, rather low concentrations of isoleucine also act partly as valine does.

b) Apparent Km values, measured in the presence of valine, vary with pH in the opposite direction to Ki values. Hill's coefficients for substrate and inhibitor reflect these findings. For threonine alone, they vary from 1.2 at pH 7 to 3 at pH 9. In the presence of valine, they remain close to 1, at all pH. Isoleucine, 0.1 mM, produces an incomplete effect compared to valine. For isoleucine inhibition, the cooperativity coefficients remain close to 3 at all pH. The molecular weight of the enzyme has been determined to be roughly 1.2 × 105, at pH 6.8 and at pH 8.7. Thermal inactivation is unimodal and fails to show desensitization of the enzyme in any of the conditions tried.

The implications of these results on the structure of the enzyme have been discussed.
The Regulation of Isoleucine‐Valine Biosynthesis in Saccharomyces cerevisiae
Authors: Magee P. T. , de Robichon‐Szulmajster H.
Published: March 2005

Regulation of activity of acetohydroxyacid synthetase has been studied. L‐Valine, one of the end‐products of the combined pathway, is the only amino acid to inhibit strongly the enzyme (Ki= 5 × 10−5 M). Sensitivity to the inhibitor is rapidly lost by heating at 35°. The desensitized enzyme is stable at this temperature. In crude extracts, the enzyme is always partly desensitized, but 100% inhibition by valine is reached when the enzyme is assayed in situ, in benzene permeabilized cells. In addition, valine inhibition is more strictly dependent upon pH than activity itself. Kinetie studies of affinity for the substrate or inhibitor show no cooperative effects and valine inhibition seems truly competitive with pyruvate. Specific feedback inhibition by valine constitutes an additional proof that the acetohydroxyacid synthetase activity characterized in studies reported in the preceding paper, is operative for valine biosynthesis.
Control of Succinate Oxidation by Succinate‐Uptake by Rat‐Liver Mitochondria
Authors: QQUAGLIARIELLO E. , PALMIERI F.
Published: March 2005

The uptake of succinate by mitochondria and the rate of respiration in the presence of succinate plus rotenone have been analysed.

In conditions in which Vmax is the same, the apparent Km for succinate is lower when respiration is activated by ion uptake than it is in the active state. The highest value is obtained in the presence of 2,4‐dinitrophenol.

Succinate uptake is maximum during ion uptake, is lower in the active state and lowest in the uncoupled state.

With increasing concentrations of uncoupler, a decrease in the intramitochondrial concentration of succinate is observed parallel to the decrease in respiration.

The inhibition of respiration caused by gramicidin under certain conditions is accompanied by a decrease in the intramitochondrial concentration of succinate.

Citrate and other substrate anions are shown to be competitive with succinate with respect to both the oxidation and the uptake of succinate.

The inhibition of respiration by citrate is less pronounced in particles than in mitochondria.

It is concluded that the rate of respiration with succinate plus rotenone as substrate is controlled by succinate uptake.