Nitrogenase MoFe-protein at 1.16 A resolution: a central ligand in the FeMo-cofactor     

Einsle O  Tezcan FA  Andrade SL  Schmid B  Yoshida M  Howard JB  Rees DC 《Science (New York, N.Y.)》2002,297(5587):1696-1700

A high-resolution crystallographic analysis of the nitrogenase MoFe-protein reveals a previously unrecognized ligand coordinated to six iron atoms in the center of the catalytically essential FeMo-cofactor. The electron density for this ligand is masked in structures with resolutions lower than 1.55 angstroms, owing to Fourier series termination ripples from the surrounding iron and sulfur atoms in the cofactor. The central atom completes an approximate tetrahedral coordination for the six iron atoms, instead of the trigonal coordination proposed on the basis of lower resolution structures. The crystallographic refinement at 1.16 angstrom resolution is consistent with this newly detected component being a light element, most plausibly nitrogen. The presence of a nitrogen atom in the cofactor would have important implications for the mechanism of dinitrogen reduction by nitrogenase.  相似文献   

The fate of Amazonian forest fragments: A 32-year investigation   总被引：2，自引：0，他引：2  

William F. Laurance  José L.C. Camargo  Regina C.C. Luizão  Susan G. Laurance  Stuart L. Pimm  Emilio M. Bruna  Philip C. Stouffer  G. Bruce Williamson  Julieta Benítez-Malvido  Heraldo L. Vasconcelos  Kyle S. Van Houtan  Charles E. Zartman  Sarah A. Boyle  Raphael K. Didham  Ana Andrade  Thomas E. Lovejoy 《Biological conservation》2011,(1):56-67

We synthesize findings to date from the world’s largest and longest-running experimental study of habitat fragmentation, located in central Amazonia. Over the past 32 years, Amazonian forest fragments ranging from 1 to 100 ha have experienced a wide array of ecological changes. Edge effects have been a dominant driver of fragment dynamics, strongly affecting forest microclimate, tree mortality, carbon storage, fauna, and other aspects of fragment ecology. However, edge-effect intensity varies markedly in space and time, and is influenced by factors such as edge age, the number of nearby edges, and the adjoining matrix of modified vegetation surrounding fragments. In our study area, the matrix has changed markedly over the course of the study (evolving from large cattle pastures to mosaics of abandoned pasture and regrowth forest) and this in turn has strongly influenced fragment dynamics and faunal persistence. Rare weather events, especially windstorms and droughts, have further altered fragment ecology. In general, populations and communities of species in fragments are hyperdynamic relative to nearby intact forest. Some edge and fragment-isolation effects have declined with a partial recovery of secondary forests around fragments, but other changes, such as altered patterns of tree recruitment, are ongoing. Fragments are highly sensitive to external vicissitudes, and even small changes in local land-management practices may drive fragmented ecosystems in markedly different directions. The effects of fragmentation are likely to interact synergistically with other anthropogenic threats such as logging, hunting, and especially fire, creating an even greater peril for the Amazonian biota.  相似文献   

Performance of four <Emphasis Type="Italic">Trichogramma</Emphasis> species (Hymenoptera: Trichogrammatidae) as biocontrol agents of <Emphasis Type="Italic">Heliothis virescens</Emphasis> (Lepidoptera: Noctuidae) under various temperature regimes     

Gilberto Santos Andrade  Dirceu Pratissoli  Leandro Pin Dalvi  Nicolas Desneux  Hugo José Gonçalves dos Santos Junior 《Journal of pest science》2011,84(3):313-320

Trichogramma spp. are major parasitoids of lepidopteran pest eggs, but there is large variation in efficacy toward a given pest among the numerous described Trichogramma species. It is important to select the Trichogramma species that most effectively parasitize and develop in target pest eggs for biological control. In this context, Trichogramma pretiosum, T. exiguum, T. atopovirilia and T. acacioi were studied in Heliothis virescens eggs under different thermal conditions. The parasitoids were reared at constant temperatures of 20, 25 and 30°C and tested at these respective temperatures, while parasitoids reared at 25°C were also tested at 20 and 30°C, for a total of 20 species–temperature combinations. About 30 H. virescens eggs were offered to the parasitoids for 24 h. Among the four species, parasitism rate by T. atopovirilia was highest at all temperature conditions, whereas T. acacioi had the lowest rates of parasitism at 25°C and 25/30°C. Parasitism ranged from 13.8 to 43.8% among all species–temperature combinations. Viability (emerged parasitoids) ranged from 80.8 to 98.4%, and was deemed satisfactory. The emergence rates of T. exiguum and T. acacioi were affected by temperature. Temperature also affected the sex ratio of T. exiguum at 25/30°C, whereas T. pretiosum and T. acacioi produced females predominantly independent of temperature. Overall, the parasitoid T. atopovirilia was the most efficient in parasitizing H. virescens eggs, though the levels of parasitism obtained might not ensure its successful use in biological control programs. The temperature-related differences in biological traits observed in the four Trichogramma species tested hint at the importance of making careful choices regarding climatic conditions where the parasitoid is going to be used when selecting a species for biological control programs.  相似文献   

Genetic variability of six indigenous goat breeds using major histocompatibility complex-associated microsatellite markers     

Patricy de Andrade Salles  Silvana C. Santos  Davide Rondina  Mathias Weller 《Journal of veterinary science (Suw?n-si, Korea)》2011,12(2):127-132

The present study aimed at analyzing the genetic variability of indigenous goat breeds (Capra hircus) using the MHC-associated microsatellite markers BF1, BM1818, BM1258, DYMS1, and SMHCC1. The following breeds were included: Chinese Xuhuai, Indian Changthangi and Pashmina, Kenyan Small East African (SEA) and Galla, and Albanian Vendi. To examine genetic variability, the levels of heterozigosity, degrees of inbreeding, and genetic differences among the breeds were analyzed. The mean number of alleles ranged from nine in the Galla to 14.5 in the Vendi breed. The mean observed heterozygosity and mean expected heterozygosity varied from 0.483 in the Vendi to 0.577 in the Galla breed, and from 0.767 in the SEA to 0.879 in the Vendi breed, respectively. Significant loss of heterozygosity (p < 0.01) indicated that these loci were not in Hardy-Weinberg equilibrium. The mean F_IS values ranged from 0.3299 in the SEA to 0.4605 in the Vendi breed with a mean value of 0.3623 in all breeds (p < 0.001). Analysis of molecular variance indicated that 7.14% and 4.74% genetic variation existed among the different breeds and geographic groups, whereas 92.86% and 95.26% existed in the breeds and the geographic groups, respectively (p < 0.001). The microsatellite marker analysis disclosed a high degree of genetic polymorphism. Loss of heterozygosity could be due to genetic drift and endogamy. The genetic variation among populations and geographic groups does not indicate a correlation of genetic differences with geographic distance.  相似文献   

Transmission electron microscopy for characterization of acrosomal damage after Percoll gradient centrifugation of cryopreserved bovine spermatozoa     

Letícia Z. Oliveira  Vera F. M. Hossepian de Lima  Marcelo A. Levenhagen  Ricarda M. dos Santos  Terezinha I. Assump??o  José O. Jacomini  André F. C. de Andrade  Rubens P. de Arruda  Marcelo E. Beletti 《Journal of veterinary science (Suw?n-si, Korea)》2011,12(3):267-272

The objective of this study was to characterize acrosomal ultrastructure following discontinuous Percoll gradient centrifugation of cryopreserved bovine sperm. Semen was collected from six bulls of different breeds and three ejaculates per bull were evaluated. Frozen semen samples were thawed and the acrosomal region of sperm cells was evaluated by transmission electron microscopy (TEM) before (n = 18) and after (n = 18) Percoll centrifugation. The evaluation of 20 sperm heads from each of the 36 samples analyzed ensured that a large number of cells were investigated. The data were subjected to analysis of variance at a level of significance of 5%. Percoll centrifugation reduced the percentage of sperm exhibiting normal acrosomes (from 61.77 to 30.24%), reduced the percentage of sperm presenting atypical acrosome reactions (from 28.38 to 4.84%) and increased the percentage of sperm exhibiting damage in the acrosome (from 6.14 to 64.26%). The percentage of sperm with typical acrosome reactions was not significantly different before (3.70%) and after (0.67%) centrifugation. TEM distinguished four different types of acrosomal status and enabled ultrastructural characterization of acrosomal injuries. The percentage of sperm exhibiting normal acrosomes decreased and damage in the acrosome was the most frequent acrosomal injury with the Percoll gradient centrifugation protocol utilized.  相似文献   

Methoxylated xanthones in the quality control of small centaury (Centaurium erythraea) flowering tops.     

Patrícia Valent?o  Paula B Andrade  Eurico Silva  Ana Vicente  Henrique Santos  M Lourdes Bastos  Rosa M Seabra 《Journal of agricultural and food chemistry》2002,50(3):460-463

In the course of a phytochemical study of the bitter tonic plant, small centaury (Centaurium erythraea), six methoxylated xanthones (1,5-hydroxy-3-methoxyxanthone, 1-hydroxy-3,5,6-trimethoxyxanthone, 1-hydroxy-3,5,6,7-tetramethoxyxanthone, 1-hydroxy-3,5,6,7,8-pentamethoxyxanthone, 1-hydroxy-3,7,8-trimethoxyxanthone and 1,8-dihydroxy-3,5,6,7-tetramethoxyxanthone) were isolated and identified by spectroscopic means (nuclear magnetic resonance, mass spectroscopy, and UV). Subsequently, a high-performance liquid chromatography/diode array detection method was developed for the determination of these and other methoxylated xanthones occurring in the chloroform extract of small centaury aerial parts. The methodology developed was applied to twelve samples, and in all of them, nine xanthones were identified and quantified. This methodology can be considered complimentary to the one proposed by the European Pharmacopoeia.  相似文献   

Klossiella equi infection in horses; sporocyst stage identified in urine     

GP REPPAS  GH COLLINS 《Australian veterinary journal》1995,72(8):316-318

  相似文献   

Microfilaraemia in Australian native birds     

GP REPPAS  WJ HARTLEY  PA GILL 《Australian veterinary journal》1995,72(9):356-357

  相似文献   

Effects of Seminal Plasma on the Number of Accessory Sperm Cells and Fertilization in Gilts     

D. Rath  K.F. Weitze  C.E. Pena Alfaro  J.C. Andrade Moura 《Reproduction in domestic animals》1989,24(3):123-127

  相似文献   

Evaluation of ciliary movement in tracheal rings to assess immunity against infectious bronchitis virus     

L F Andrade  P Villegas  O J Fletcher  R Laudencia 《Avian diseases》1982,26(4):805-815

Chickens vaccinated at one and 14 days of age with a live vaccine containing the Massachusetts and Connecticut strains of infectious bronchitis virus were protected against challenge with a Massachusetts strain administered at 5 weeks of age. The virus recovery method in which tracheal swabs taken 4 days post-challenge were used to inoculate chicken embryos was compared with the method based on ciliary activity in tracheal explants. The results showed that evaluation of ciliary activity effectively measured immunity to infectious bronchitis virus. Serological results obtained in a microneutralization test using chicken embryo kidney cells correlated with the immune status of the birds as well as with the alpha neutralization results obtained using chicken embryos.  相似文献