Architecture of a fungal fatty acid synthase at 5 A resolution     

Jenni S  Leibundgut M  Maier T  Ban N 《Science (New York, N.Y.)》2006,311(5765):1263-1267

All steps of fatty acid synthesis in fungi are catalyzed by the fatty acid synthase, which forms a 2.6-megadalton alpha6beta6 complex. We have determined the molecular architecture of this multienzyme by fitting the structures of homologous enzymes that catalyze the individual steps of the reaction pathway into a 5 angstrom x-ray crystallographic electron density map. The huge assembly contains two separated reaction chambers, each equipped with three sets of active sites separated by distances up to approximately 130 angstroms, across which acyl carrier protein shuttles substrates during the reaction cycle. Regions of the electron density arising from well-defined structural features outside the catalytic domains separate the two reaction chambers and serve as a matrix in which domains carrying the various active sites are embedded. The structure rationalizes the compartmentalization of fatty acid synthesis, and the spatial arrangement of the active sites has specific implications for our understanding of the reaction cycle mechanism and of the architecture of multienzymes in general.  相似文献   

Naive and memory CD4+ T cell survival controlled by clonal abundance   总被引：1，自引：0，他引：1  

Hataye J  Moon JJ  Khoruts A  Reilly C  Jenkins MK 《Science (New York, N.Y.)》2006,312(5770):114-116

Immunity to a plethora of microbes depends on a diverse repertoire of na?ve lymphocytes and the production of long-lived memory cells. We present evidence here that low clonal abundance in a polyclonal repertoire favors the survival and activation of na?ve CD4(+) T cells as well as the survival of their memory cell progeny. The inverse relation between clonal frequency and survival suggests that intraclonal competition could help maintain an optimally diverse repertoire of T cells and an optimal environment for the generation of long-lived memory cells.  相似文献   

Impact of pH on the kinetics of acrylamide formation/elimination reactions in model systems     

De Vleeschouwer K  Van der Plancken I  Van Loey A  Hendrickx ME 《Journal of agricultural and food chemistry》2006,54(20):7847-7855

The effect of pH on acrylamide formation and elimination kinetics was studied in an equimolar (0.1 M) asparagine-glucose model system in phosphate or citrate buffer, heated at temperatures between 120 and 200 degrees C. To describe the experimental data, a simplified kinetic model was proposed and kinetic parameters were estimated by combined nonlinear regression and numerical integration on the data obtained under nonisothermal conditions. The model was subsequently validated in a more realistic potato-based matrix with varying pH. By increasing acidity, the reaction rate constants at T(ref) (160 degrees C) for both acrylamide formation and elimination can significantly be reduced, whereas the temperature dependence of both reaction rate constants increases. The introduction of a lyophilized potato matrix (20%) did not affect the acrylamide formation reaction rate constant at reference temperature (160 degrees C) as compared to the asparagine-glucose model system; the elimination rate constant at T(ref), on the contrary, was almost doubled.  相似文献   

Molecular and phenotypical characterization of Clostridium perfringens isolates from poultry flocks with different disease status   总被引：1，自引：0，他引：1  

Gholamiandekhordi AR  Ducatelle R  Heyndrickx M  Haesebrouck F  Van Immerseel F 《Veterinary microbiology》2006,113(1-2):143-152

Due to the diminished use of growth-promoting antibiotics in the European Union, Clostridium perfringens induced necrotic enteritis and subclinical disease have become important threats to poultry health. A study was set up to genotypically and phenotypically characterise C. perfringens isolates from poultry flocks with different health status. Animals from healthy flocks were sampled by cloacal swabs, while intestinal and liver samples of animals suffering from necrotic enteritis were analysed. A total of 27 isolates was obtained from 23 broiler flocks without clinical problems and 36 isolates were obtained from 8 flocks with clinical problems. Using PFGE typing, high genetic diversity was detected between isolates from different flocks. Isolates derived from flocks where disease outbreaks occurred were clonal within each flock, but each flock harboured a different clone. All isolates were of toxin type A. Isolates from 5 out of 35 PFGE types carried the cpb2 gene, encoding the beta2 toxin, and isolates from 2 out of 35 PFGE types harboured the cpe gene, encoding the enterotoxin. In vitro alpha toxin production for all isolates was quantified by enzyme-linked immunosorbent assay. It was shown that in vitro alpha toxin production of C. perfringens isolates from diseased flocks was not higher than in vitro alpha toxin production from isolates derived from healthy flocks.  相似文献   

Mapping African Animal Trypanosomosis risk from the sky     

Bouyer J  Guerrini L  Desquesnes M  de la Rocque S  Cuisance D 《Veterinary research》2006,37(5):633-645

In Burkina Faso, African Animal Trypanosomosis (AAT) is still a major hindrance to cattle breeding, especially in the Mouhoun river basin, which was identified as a priority area for tsetse control. The attempt of the present work was to assess the abundance of tsetse flies and AAT risk using remote sensing coupled to field environmental data, along a Mouhoun river section of 234 km long, harbouring an open riverine forest where G. tachinoides Westwood is the predominant tsetse species. The water course was classified into three epidemiological landscapes, corresponding to a "disturbed", "natural" and finally "border" vegetal formation at the interface of the two formers. Using the mean number of infected flies by trap and by day as a risk indicator, the border landscape was found to be 5.4 (1.3-12.0) and 15.8 (4.7-41.6) times more risky than the natural and disturbed ones respectively. These results led to propose that a campaign against tsetse, undertaken by a development project called PAEOB (Projet d'Appui à l'Elevage dans l'Ouest du Burkina Faso), should be focussed on only 34% of the hydrographic network.  相似文献   

Cross-modality of texture and aroma perception is independent of orthonasal or retronasal stimulation     

Visschers RW  Jacobs MA  Frasnelli J  Hummel T  Burgering M  Boelrijk AE 《Journal of agricultural and food chemistry》2006,54(15):5509-5515

To assess the influence of orthonasal and retronasal stimulation on cross-modal interactions between texture and flavor perception of food, a series of experiments have been conducted. Healthy human subjects were exposed to strawberry aroma pulses delivered by a computer-controlled stimulator based on air dilution olfactometry. Just prior to exposure to the aroma, the human subjects consumed water, custard, or protein gels with different textures without any added aroma. The aroma was delivered as a sequence of aroma pulses, in either an orthonasal or a retronasal fashion. The retronasal presentation of aroma with concomitant presentation of texture is thought to more closely mimick the in vivo flavor release of semisolid food products as compared to orthonasal stimulation. The time between oral consumption of the food, including swallowing, and the exposure to the aroma varied between 0.5 and 6.5 s. The subjects rated the intensity of the strawberry aroma. It was observed that the intensity of aroma decreased with increasing firmness of the food that was consumed. Aroma pulses delivered 6.5 s after swallowing were perceived as being more intense as compared to aroma pulses delivered immediately after swallowing. In conjunction with late delivery, the effect cross-modal interactions apparently decreased. Significantly higher odor intensities were reported for the aroma stimuli supplied orthonasally in comparison to retronasal administration. The observed cross-modal effect of texture on aroma intensity was not significantly altered by the mode of aroma delivery, i.e., orthonasal or retronasal stimulus administration.  相似文献   

Infrared spectroscopy of comet 81P/Wild 2 samples returned by Stardust     

Keller LP  Bajt S  Baratta GA  Borg J  Bradley JP  Brownlee DE  Busemann H  Brucato JR  Burchell M  Colangeli L  d'Hendecourt L  Djouadi Z  Ferrini G  Flynn G  Franchi IA  Fries M  Grady MM  Graham GA  Grossemy F  Kearsley A  Matrajt G  Nakamura-Messenger K  Mennella V  Nittler L  Palumbo ME  Stadermann FJ  Tsou P  Rotundi A  Sandford SA  Snead C  Steele A  Wooden D  Zolensky M 《Science (New York, N.Y.)》2006,314(5806):1728-1731

Infrared spectra of material captured from comet 81P/Wild 2 by the Stardust spacecraft reveal indigenous aliphatic hydrocarbons similar to those in interplanetary dust particles thought to be derived from comets, but with longer chain lengths than those observed in the diffuse interstellar medium. Similarly, the Stardust samples contain abundant amorphous silicates in addition to crystalline silicates such as olivine and pyroxene. The presence of crystalline silicates in Wild 2 is consistent with mixing of solar system and interstellar matter. No hydrous silicates or carbonate minerals were detected, which suggests a lack of aqueous processing of Wild 2 dust.  相似文献   

Organics captured from comet 81P/Wild 2 by the Stardust spacecraft     

Sandford SA  Aléon J  Alexander CM  Araki T  Bajt S  Baratta GA  Borg J  Bradley JP  Brownlee DE  Brucato JR  Burchell MJ  Busemann H  Butterworth A  Clemett SJ  Cody G  Colangeli L  Cooper G  D'Hendecourt L  Djouadi Z  Dworkin JP  Ferrini G  Fleckenstein H  Flynn GJ  Franchi IA  Fries M  Gilles MK  Glavin DP  Gounelle M  Grossemy F  Jacobsen C  Keller LP  Kilcoyne AL  Leitner J  Matrajt G  Meibom A  Mennella V  Mostefaoui S  Nittler LR  Palumbo ME  Papanastassiou DA  Robert F  Rotundi A  Snead CJ  Spencer MK  Stadermann FJ  Steele A 《Science (New York, N.Y.)》2006,314(5806):1720-1724

Organics found in comet 81P/Wild 2 samples show a heterogeneous and unequilibrated distribution in abundance and composition. Some organics are similar, but not identical, to those in interplanetary dust particles and carbonaceous meteorites. A class of aromatic-poor organic material is also present. The organics are rich in oxygen and nitrogen compared with meteoritic organics. Aromatic compounds are present, but the samples tend to be relatively poorer in aromatics than are meteorites and interplanetary dust particles. The presence of deuterium and nitrogen-15 excesses suggest that some organics have an interstellar/protostellar heritage. Although the variable extent of modification of these materials by impact capture is not yet fully constrained, a diverse suite of organic compounds is present and identifiable within the returned samples.  相似文献   

Astronomy. Cosmic rays track the rotation of the Milky Way     

Duldig M 《Science (New York, N.Y.)》2006,314(5798):429-430

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Urodynamic and morphologic changes in the lower portion of the urogenital tract after administration of estriol alone and in combination with phenylpropanolamine in sexually intact and spayed female dogs     

Hamaide AJ  Grand JG  Farnir F  Le Couls G  Snaps FR  Balligand MH  Verstegen JP 《American journal of veterinary research》2006,67(5):901-908

OBJECTIVE: To compare the urodynamic and morphologic effects of the administration of estriol alone and in combination with phenylpropanolamine on the lower portion of the urogenital tract in female dogs. ANIMALS: 3 sexually intact and 3 spayed female Beagles without urinary incontinence. PROCEDURE: Dogs received estriol (2 mg, PO) once daily for 7 days followed by estriol (2 mg, PO) and phenylpropanolamine (1.5 mg/kg, PO) once daily for 7 days. Urethral pressure profilometry, diuresis cystometry, and vaginourethrography were performed before treatment (day 0) and at days 7 and 14. The maximum urethral pressure (MUP) and closure pressure (MUCP), urethral functional and anatomic profile lengths, integrated pressure (IP), plateau, distance before MUP, maximum meatus pressure, threshold pressure, threshold volume, compliance, urethral length, and vaginal length and width were measured. RESULTS: Before treatment, no urodynamic differences were observed between the 2 groups; however, vaginal length and width were significantly shorter in spayed dogs. Compared with day 0 values, estriol treatment significantly increased MUP, MUCP, and IP values at day 7, but at day 14, this effect decreased despite phenylpropanolamine administration. No morphologic changes from baseline were detected after either treatment in any dog. CONCLUSIONS AND CLINICAL RELEVANCE: Data suggest that estriol mainly acts on the urethral sphincter mechanism by increasing urethral resistance in sexually intact and spayed female dogs without urinary incontinence. Administration of estriol and phenylpropanolamine did not increase the urethral resistance more than estriol alone. The urodynamic effects of estriol in female dogs with urinary incontinence remain to be elucidated.  相似文献