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排序方式: 共有181条查询结果,搜索用时 265 毫秒
171.
将C群脑膜炎球菌粗多糖的纯化改进为用1:1容量冷酚提取的生产工艺。结果表明,改进后的方法去除蛋白质效果同样能够达到《中国药典》2005版(三部)的要求,总体结果优于改进前。同时能扩大处理量而降低了生产成本,适合规模化生产。 相似文献
172.
Background
We recently observed an association of resistance with a certain enteropathogenic Escherichia coli (EPEC) serotypes and identified a conjugative plasmid, similar to plasmid pED208, that was conserved among archival O111:H2/NM and O119:H2 strains of diverse geographical origin. In this study, we sought to determine the prevalence and distribution of this plasmid among a collection of EPEC isolates from Brazil, as well as to study the susceptibilities of these isolates to antimicrobial agents. 相似文献173.
174.
Scott KM Sievert SM Abril FN Ball LA Barrett CJ Blake RA Boller AJ Chain PS Clark JA Davis CR Detter C Do KF Dobrinski KP Faza BI Fitzpatrick KA Freyermuth SK Harmer TL Hauser LJ Hügler M Kerfeld CA Klotz MG Kong WW Land M Lapidus A Larimer FW Longo DL Lucas S Malfatti SA Massey SE Martin DD McCuddin Z Meyer F Moore JL Ocampo LH Paul JH Paulsen IT Reep DK Ren Q Ross RL Sato PY Thomas P Tinkham LE Zeruth GT 《PLoS biology》2006,4(12):e383
Presented here is the complete genome sequence of Thiomicrospira crunogena XCL-2, representative of ubiquitous chemolithoautotrophic sulfur-oxidizing bacteria isolated from deep-sea hydrothermal vents. This gammaproteobacterium has a single chromosome (2,427,734 base pairs), and its genome illustrates many of the adaptations that have enabled it to thrive at vents globally. It has 14 methyl-accepting chemotaxis protein genes, including four that may assist in positioning it in the redoxcline. A relative abundance of coding sequences (CDSs) encoding regulatory proteins likely control the expression of genes encoding carboxysomes, multiple dissolved inorganic nitrogen and phosphate transporters, as well as a phosphonate operon, which provide this species with a variety of options for acquiring these substrates from the environment. Thiom. crunogena XCL-2 is unusual among obligate sulfur-oxidizing bacteria in relying on the Sox system for the oxidation of reduced sulfur compounds. The genome has characteristics consistent with an obligately chemolithoautotrophic lifestyle, including few transporters predicted to have organic allocrits, and Calvin-Benson-Bassham cycle CDSs scattered throughout the genome. 相似文献
175.
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177.
Alexander V. Pushkin Frederick A. Eiserling Cheryl A. Kerfeld J.Philip Thornber 《FEMS microbiology letters》1993,113(2):167-173
Abstract Porphyromonas gingivalis produces a trypsin-like enzyme, Protease I, which is thought to be an important virulence determinant of the organism in adult periodontal disease. Protease I is transiently inhibited by physiological inhibitors of human thrombin. The aim of the present work was to establish whether Protease I was able to mimic thrombin by activation of the thrombin receptor on human platelets. Protease I caused true platelet activation at concentrations comparable to thrombin as measured by aggregometry, morphology and fluorescence flow cytometric analysis of CD63 expression. The effect was blocked by protease inhibitors but not by anti-thrombin receptor antibodies which, by contrast, blocked platelet activation by thrombin. We conclude that the activation of platelets by P. gingivalis Protease I involves proteolysis, but not scission of the thrombin cleavage site of the thrombin receptor. 相似文献
178.
Molecular evolution of olfactomedin 总被引:2,自引:0,他引:2
Olfactomedin is a secreted polymeric glycoprotein of unknown function,
originally discovered at the mucociliary surface of the amphibian olfactory
neuroepithelium and subsequently found throughout the mammalian brain. As a
first step toward elucidating the function of olfactomedin, its
phylogenetic history was examined to identify conserved structural motifs.
Such conserved motifs may have functional significance and provide targets
for future mutagenesis studies aimed at establishing the function of this
protein. Previous studies revealed 33% amino acid sequence identity between
rat and frog olfactomedins in their carboxyl terminal segments. Further
analysis, however, reveals more extensive homologies throughout the
molecule. Despite significant sequence divergence, cysteines essential for
homopolymer formation such as the CXC motif near the amino terminus are
conserved, as is the characteristic glycosylation pattern, suggesting that
these posttranslational modifications are essential for function.
Furthermore, evolutionary analysis of a region of 53 amino acids of fish,
frog, rat, mouse, and human olfactomedins indicates that an ancestral
olfactomedin gene arose before the evolution of terrestrial vertebrates and
evolved independently in teleost, amphibian, and mammalian lineages.
Indeed, a distant olfactomedin homolog was identified in Caenorhabditis
elegans. Although the amino acid sequence of this invertebrate protein is
longer and highly divergent compared with its vertebrate homologs, the
protein from C. elegans shows remarkable similarities in terms of conserved
motifs and posttranslational modification sites. Six universally conserved
motifs were identified, and five of these are clustered in the carboxyl
terminal half of the protein. Sequence comparisons indicate that evolution
of the N-terminal half of the molecule involved extensive insertions and
deletions; the C-terminal segment evolved mostly through point mutations,
at least during vertebrate evolution. The widespread occurrence of
olfactomedin among vertebrates and invertebrates underscores the notion
that this protein has a function of universal importance. Furthermore,
extensive modification of its N-terminal half and the acquisition of a
C-terminal SDEL endoplasmic-reticulum- targeting sequence may have enabled
olfactomedin to adopt new functions in the mammalian central nervous
system.
相似文献
179.
Jan Zarzycki Onur Erbilgin Cheryl A. Kerfeld 《Applied and environmental microbiology》2015,81(24):8315-8329
Bacterial microcompartments (BMCs) are proteinaceous organelles encapsulating enzymes that catalyze sequential reactions of metabolic pathways. BMCs are phylogenetically widespread; however, only a few BMCs have been experimentally characterized. Among them are the carboxysomes and the propanediol- and ethanolamine-utilizing microcompartments, which play diverse metabolic and ecological roles. The substrate of a BMC is defined by its signature enzyme. In catabolic BMCs, this enzyme typically generates an aldehyde. Recently, it was shown that the most prevalent signature enzymes encoded by BMC loci are glycyl radical enzymes, yet little is known about the function of these BMCs. Here we characterize the glycyl radical enzyme-associated microcompartment (GRM) loci using a combination of bioinformatic analyses and active-site and structural modeling to show that the GRMs comprise five subtypes. We predict distinct functions for the GRMs, including the degradation of choline, propanediol, and fuculose phosphate. This is the first family of BMCs for which identification of the signature enzyme is insufficient for predicting function. The distinct GRM functions are also reflected in differences in shell composition and apparently different assembly pathways. The GRMs are the counterparts of the vitamin B12-dependent propanediol- and ethanolamine-utilizing BMCs, which are frequently associated with virulence. This study provides a comprehensive foundation for experimental investigations of the diverse roles of GRMs. Understanding this plasticity of function within a single BMC family, including characterization of differences in permeability and assembly, can inform approaches to BMC bioengineering and the design of therapeutics. 相似文献
180.
Bacterial Microcompartments (BMCs) are proteinaceous organelles that encapsulate critical segments of autotrophic and heterotrophic metabolic pathways; they are functionally diverse and are found across 23 different phyla. The majority of catabolic BMCs (metabolosomes) compartmentalize a common core of enzymes to metabolize compounds via a toxic and/or volatile aldehyde intermediate. The core enzyme phosphotransacylase (PTAC) recycles Coenzyme A and generates an acyl phosphate that can serve as an energy source. The PTAC predominantly associated with metabolosomes (PduL) has no sequence homology to the PTAC ubiquitous among fermentative bacteria (Pta). Here, we report two high-resolution PduL crystal structures with bound substrates. The PduL fold is unrelated to that of Pta; it contains a dimetal active site involved in a catalytic mechanism distinct from that of the housekeeping PTAC. Accordingly, PduL and Pta exemplify functional, but not structural, convergent evolution. The PduL structure, in the context of the catalytic core, completes our understanding of the structural basis of cofactor recycling in the metabolosome lumen. 相似文献