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191.
T K Sixma A Aguirre A C Terwisscha van Scheltinga E S Wartna K H Kalk W G Hol 《FEBS letters》1992,305(2):81-85
A new native crystal form of heat-labile enterotoxin (LT) has two AB5 complexes in the asymmetric unit with different orientations of the A subunit with respect to the B pentamer. Comparison with other crystal forms of LT shows that there is considerable conformational freedom for orientating the A subunit with respect to the B pentamer. The rotations of A in different crystal forms do not follow one specific axis, but most of them share a hinge point, close to the main interaction area between A and B5. Analysis of the two high-resolution structures available shows that these rotations cause very little change in the actual interactions between A and B5. 相似文献
192.
Photosynthetic pigment composition was studied in batch cultures of Heterocapsa sp. and Olisthodiscus luteus growing exponentially in a 12:12 light:dark cycle. Both species divided in the dark. The synthesis of pigments was continuous for both species. However for chlorophyll c and peridinin, in Heterocapsa sp., and chlorophyll c and fucoxanthin, in O. luteus, (pigments belonging to light harvesting complexes) the synthesis was significantly higher during the light period. Concentrations per total cell volume (TCV) of chlorophyll a, chlorophyll c, peridinin and diadinoxanthin in Heterocapsa sp., and chlorophyll a, chlorophyll c, fucoxanthin and violaxanthin in O. luteus, showed a maximum at the onset of light and decreased during the light period. The values of the chlorophyll a:chlorophyll c, chlorophyll a:peridinin and chlorophyll a:fucoxanthin ratios are compared with data reported in the literature. 相似文献
193.
C2‐symmetric sulfonamides as homogeneous and heterogeneous organocatalysts that mimic enzymes in enantioselective Michael additions 下载免费PDF全文
Harold Cruz Felipe A. Servín Domingo Madrigal Daniel Chávez Sergio Perez‐Sicairos Gerardo Aguirre Andrew L. Cooksy Ratnasamy Somanathan 《Chirality》2018,30(8):1036-1044
Herein, we report the synthesis of C2‐symmetric sulfonamides as homogeneous and heterogeneous organocatalysts and their application in the enantioselective conjugate 1,4‐Michael addition of carbonylic nucleophiles to β‐nitrostyrene. Organocatalysts hydrogen bond to β‐nitrostyrene and enamine in the transition state, mimicking an enzyme leading to final products in high yields (up to 98%) and good enantioselectivities (up to 96%). In addition, these results were supported by density functional calculations. 相似文献
194.
Reaction heat measurements in the enzymatic hydrolysis reaction of penicillin GK to obtain 6-APA 总被引:1,自引:0,他引:1
R.D. Godoy L.F. Sanabria A. Gómez Aguirre L. Giraldo A. Gómez Ordoñez G. Buitrago 《Enzyme and microbial technology》1996,19(8):585-589
The purpose of this study was to measure heats involved in the hydrolysis process for the industrial production of 6-aminopenicillanic acid (6-APA) using dynamic calorimetry techniques. The experimental design was planned using Hess' law. The information derived from the calorimeter was correlated mathematically to determine the heat released during enzymatic hydrolysis. This is important for temperature control systems and reactor design. The results obtained with the calorimetric measurements at 308 K and pH 7.5 are the penicillin hydrolysis, ΔHhydrol, at 35.9 ± 5.7 kJ mol−1 and phenyl acetic acid neutralization, ΔHneut, at −47.1 ± 3.8 kJ mol−1. 相似文献
195.
Abstract. A syntaxonomic study of the major plant communities in neotropical North American deserts (Sonoran, Mojave and Baja California Deserts) is presented. The field method of the Braun-Blanquet approach was combined with a numerical syntaxonomical analysis (cluster analysis and principal coordinate ordination). 21 associations are described for the first time: Ambrosio chenopodifoliae-Larreetum tridentatae, Acamptopappo sphaerocephali-Larreetum tridentatae, Hymenocleo monogyrae-Baccharidetum glutinosae, Bergerocacto emoryi-Agavetum shawii, Burseretum hindsianomicrophyllae, Cercidio microphylli-Carnegieetum giganteae, Bursero microphyllae-Cyrtocarpetum edulis, Hymenocleo salsolae-Daleetum spinosae, Echinocereo engelmannii-Agavetum deserti, Euphorbio californicae-Fouquierietum diguetii, Fouquierio splendentis-Larreetum tridentatae, Agavo cerulatae-Idrietum columnaris, Mascagnio macropterae-Lysilometum candidae, Maytenetum phyllanthoidis, Opuntio basilaris-Larreetum tridentatae, Prosopidetum torreyanae, Roso minutifoliae-Aesculetum parryi, Opuntio taponae-Agavetum subcerulatae, Tidestromio oblongifoliae-Atriplicetum hymenelytrae, Eurotio lanatae-Larreetum tridentatae and Yucco validae-Fouquierietum diguetii. Some associations include subassociations. Ecological, biogeographical and floristic bioclimatic data are given for each association. 相似文献
196.
The area between Ensenada and EI Rosario (Baja California, Mexico) has long been considered as a transitional zone in which two great ecoclimatic regions (Mediterranean and Tropical-Desert) overlap. The floristic and biotypical diversity of this area was evaluated by analyzing its shrubland formations from a phytosociological point of view. This phytosociological study, carried out according to the Braun-Blanquet method and supported by cluster analysis, describes sixteen shrubland associations from Northwestern Baja California.Floristic diversity of the transitional zone was evaluated using two indices, endemic value (EV) and endemic community value (ECV), which are related to the degree of endemism in the flora and plant associations. The phytosociological analysis showed that the high number of shrubland associations found in this area reflected its transitional character. The closer the associations are to the transitional zone, the higher their biotypical and floristic diversity.Abbreviations ADE
Adenostoma fasciculatum
- AES
Fraxinus trifoliata-Aesculus parryi
- BER
Bergerocactus emoryi-Agave shawii
- DES
Echinocereus engelmannii-Agave deserti
- ENC
Viguiera deltoidea-Encelia asperifolia
- EUR
Eurotia lanata-Yucca schidigera
- FOU
Agave cerulata-Fouquieria columnaris
- FRA
Atriplex julacea-Frankenia palmeri
- HYM
Baccharis glutinosa-Hymenoclea monogyra
- KEC
Clematis lasiantha-Keckiella antirrhinoides
- LAR
Ambrosia chenopodifolia-Larrea tridentata
- LYC
Ephedra californica-Lycium brevipes
- MAH
Malosma laurina-Heteromeles arbutifolia
- MUN
Salvia munzii-Artemisia californica
- ROS
Rosa minutifolia-Aesculus parryi
- SAL
Salvia apiana-Viguiera laciniata 相似文献
197.
198.
Cryptosporidium sp. Infections in Green Turtles, Chelonia mydas, as a Potential Source of Marine Waterborne Oocysts in the Hawaiian Islands 总被引:2,自引:0,他引:2 下载免费PDF全文
T. K. Graczyk G. H. Balazs T. Work A. A. Aguirre D. M. Ellis S. Murakawa R. Morris 《Applied microbiology》1997,63(7):2925-2927
For the first time, Cryptosporidium sp. oocysts were identified in fecal and intestinal samples from free-ranging marine turtles, Chelonia mydas, from the Hawaiian Islands. The oocysts produced positive reactions with commercial test kits recommended for the detection of human-infectious waterborne oocysts of Cryptosporidium parvum. 相似文献
199.
Mikel Valle Jose Maria Valpuesta Jose L. Carrascosa Javier Tamayo Ricardo Garcia 《Journal of structural biology》1996,116(3):390-398
The connector of bacteriophage φ29 is involved in DNA packaging during viral morphogenesis and we have studied itsin vitrobinding to DNA using either linear or circular DNA. The protein–DNA complexes have been analyzed by transmission electron microscopy (TEM) and by atomic force microscopy (AFM) of samples directly deposited on mica. TEM showed the presence of a specific binding due to the interaction of the protein with the free ends of the DNA. The study of these samples by AFM showed two major types of morphologies: The interaction of the connector with circular DNA revealed that the strands of DNA that enter and exit the protein complex form an angle with a mean value of 132°. Nevertheless, when the connector was incubated with linear DNA (and later circularized), there was an additional bend angle of about 168°. Further morphological analysis of the latter samples by AFM revealed a structure of the protein–DNA complex consistent with the DNA traversing the connector, probably through the inner channel. On the other hand, images from the samples obtained by incubation of the connector with circular DNA were consistent with an interaction of the DNA with the outer side of the connector. 相似文献
200.
This phytosociological study, carried out according to the Braun–Blanquet method and supported by cluster analysis, describes Walter's zonobiomes along the North American Pacific coast between the California–Oregon state border and Alaska (USA), including some interior zones of British Columbia and the Yukon Territory (Canada). Twenty two floristic associations are identified and each is characterized by a unique floristic combination, a distinctive geographical range and particular bioclimatic or edaphic conditions. 相似文献