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1.
The erythrocytes of blood clams (arcidae) are flattened, elliptical, and nucleated. They contain elliptical marginal bands (MBs) of microtubules, each physically associated with a pair of centrioles marginal bands (MBs) of microtubles, each physically associated with a pair of centrioles (Cohen, W., and I. Nemhauser, 1980, J. Cell Biol., 86:286-291). The MBs were found to be cold labile in living cells, disappearing within 1-2 h at 0 degrees C. After the cells had been rewarmed for 1-2 h, continuous MBs with associated centrioles were once again present. Time-course studies utilizing phase contrast, antitubulin immunofluorescence, and electron microscopy of cytoskeletons prepared during rewarming revealed structural evidence of centriole participation in MB reassembly. At the earliest stage of reassembly, a continuous MB was not present. Instead, relatively short and straight microtubules focused on a pointed centriolar “pole,” and none were present elsewhere in the cytoskeleton. Thin continuous MBs then formed, still pointed in the centriolar region. Subsequently, the MBs regained ellipticity, with their thickness gradually increasing but not reaching that of controls even after several hours of rewarming. At these later time points, microtubules still radiated from the centrioles and joined the MBs some distance away. In the presence of 0.1 mM colchicines, MB reassembly was arrested at the pointed stage. Electron microscopic observations indicate that pericentriolar material is involved in microtubule nucleation in this system, rather than the centriolar triplets directly. The results suggest a model in which the centrioles and associated material nucleate assembly and growth of microtubules in diverging directions around the cell periphery. Microtubules of opposite polarity would then pass each other at the end of the cell distal to the centrioles, with continued elongation eventually closing the MB ellipse behind the centriole pair. 相似文献
2.
Tolbutamide and phenytoin hydroxylations by cDNA-expressed human liver cytochrome P4502C9 总被引:7,自引:0,他引:7
M E Veronese P I Mackenzie C J Doecke M E McManus J O Miners D J Birkett 《Biochemical and biophysical research communications》1991,175(3):1112-1118
A human cytochrome P4502C9 cDNA clone has been isolated from a human liver bacteriophage Lambda gt11 library using oligonucleotide probes. Expression of the 1762 base pair cDNA in COS cells demonstrated that the encoded enzyme has a molecular mass of 55 kDa as determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The expressed enzyme catalysed the methylhydroxylation of tolbutamide with an apparent Km of 131.7 microM, similar to that observed in human liver microsomes. P4502C9 also catalysed the 4-hydroylation of phenytoin, and inhibition experiments demonstrated that phenytoin was a competitive inhibitor of tolbutamide hydroxylation with an apparent Ki of 19.1 microM. Sulphaphenazole was a potent inhibitor of the expressed enzyme with respect to both tolbutamide and phenytoin hydroxylations. These data demonstrate that a single isozyme can catalyse the hydroxylations of both tolbutamide and phenytoin, and suggest that both reactions are mediated by the same isozyme(s) of cytochrome P450 in human liver. 相似文献
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4.
Alessandro S Guimarães Filipe B Carmo Marcos B Heinemann Ricardo WD Portela Roberto Meyer Andrey P Lage Núbia Seyffert Anderson Miyoshi Vasco Azevedo Aurora MG Gouveia 《BMC veterinary research》2011,7(1):1-5
Background
Multiple congenital ocular anomalies (MCOA) syndrome is a hereditary congenital eye defect that was first described in Silver colored Rocky Mountain horses. The mutation causing this disease is located within a defined chromosomal interval, which also contains the gene and mutation that is associated with the Silver coat color (PMEL17, exon 11). Horses that are homozygous for the disease-causing allele have multiple defects (MCOA-phenotype), whilst the heterozygous horses predominantly have cysts of the iris, ciliary body or retina (Cyst-phenotype). It has been argued that these ocular defects are caused by a recent mutation that is restricted to horses that are related to the Rocky Mountain Horse breed. For that reason we have examined another horse breed, the Icelandic horse, which is historically quite divergent from Rocky Mountain horses.Results
We examined 24 Icelandic horses and established that the MCOA syndrome is present in this breed. Four of these horses were categorised as having the MCOA-phenotype and were genotyped as being homozygous for the PMEL17 mutation. The most common clinical signs included megaloglobus, iris stromal hypoplasia, abnormal pectinate ligaments, iridociliary cysts occasionally extending into the peripheral retina and cataracts. The cysts and pectinate ligament abnormalities were observed in the temporal quadrant of the eyes. Fourteen horses were heterozygous for the PMEL17 mutation and were characterized as having the Cyst-phenotype with cysts and occasionally curvilinear streaks in the peripheral retina. Three additional horses were genotyped as PMEL17 heterozygotes, but in these horses we were unable to detect cysts or other forms of anomalies. One eye of a severely vision-impaired 18 month-old stallion, homozygous for the PMEL17 mutation was examined by light microscopy. Redundant duplication of non-pigmented ciliary body epithelium, sometimes forming cysts bulging into the posterior chamber and localized areas of atrophy in the peripheral retina were seen.Conclusions
The MCOA syndrome is segregating with the PMEL17 mutation in the Icelandic Horse population. This needs to be taken into consideration in breeding decisions and highlights the fact that MCOA syndrome is present in a breed that are more ancient and not closely related to the Rocky Mountain Horse breed. 相似文献5.
6.
Kuklish SL Backer RT Briner K Doecke CW Husain S Mullaney JT Ornstein PL Zgombick JM O'Brien TP Fisher MJ 《Bioorganic & medicinal chemistry letters》2006,16(14):3843-3846
Homologation and cyclization back to the chiral methine of compound 3 yields achiral 4,4-disubstituted piperidine privileged structures (e.g., 8a) useful in the construction of melanocortin 4 receptor (MC4R) ligands. The piperidine nitrogen was replaced with carbon, oxygen, sulfur, and sulfone with minor erosion of binding. The methyl cyclohexane substituent was the most potent while significant affinity was still seen for smaller lipophilic groups such as ethyl. 相似文献
7.
Goring DR Banks P Fallis L Baszczynski CL Beversdorf WD Rothstein SJ 《The Plant journal : for cell and molecular biology》1992,2(6):999-1003
We have previously described a developmentally regulated mRNA in maize that accumulates in mature embryos and is involved in a variety of stress responses in the plant. The sequence of the encoded 16 kDa protein (MA16) predicts that it is an RNA-binding protein, since it possesses a ribonucleoprotein consensus sequence-type RNA-binding domain (CS-RBD). To assess the predicted RNA binding property of the protein and as a starting point to characterize its function we have used ribohomopolymer-binding assays. Here we show that the MA16-encoded protein binds preferentially to uridine- and guanosine-rich RNAs. In light of these results a likely role for this protein in RNA metabolism during late embryogenesis and in the stress response is discussed. 相似文献
8.
Microorganisms are associated with a variety of ancient geological materials. However, conclusive proof that these organisms
are as old as the geological material and not more recent introductions has generally been lacking. Over the years, numerous
reports of the isolation of ancient bacteria from geological materials have appeared. Most of these have suffered from the
fact that the protocol for the surface sterilization of the sample was either poorly defined, inadequate or rarely included
data to validate the overall effectiveness of the sterilization protocol. With proper sterility validation and isolation protocol,
a legitimate claim for the isolation of an ancient microbe can be made. Biochemical, physiological, or morphological data
indicate that these ancient microbes are not significantly different from modern isolates. As the role (decomposition) of
modern and ancient microbes has not changed over time, it is probably unreasonable to expect these organisms to be vastly
different. A discussion on the reasons for the homogeneity of ancient and modern microbes is presented. Journal of Industrial Microbiology & Biotechnology (2002) 28, 32–41 DOI: 10.1038/sj/jim/7000174
Received 20 May 2001/ Accepted in revised form 16 June 2001 相似文献
9.
Lars Behrendt Anthony WD Larkum Anders Norman Klaus Qvortrup Min Chen Peter Ralph S?ren J S?rensen Erik Trampe Michael Kühl 《The ISME journal》2011,5(6):1072-1076
Cyanobacteria in the genus Acaryochloris are the only known oxyphototrophs that have exchanged chlorophyll a (Chl a) with Chl d as their primary photopigment, facilitating oxygenic photosynthesis with near infrared (NIR) light. Yet their ecology and natural habitats are largely unknown. We used hyperspectral and variable chlorophyll fluorescence imaging, scanning electron microscopy, photopigment analysis and DNA sequencing to show that Acaryochloris-like cyanobacteria thrive underneath crustose coralline algae in a widespread endolithic habitat on coral reefs. This finding suggests an important role of Chl d-containing cyanobacteria in a range of hitherto unexplored endolithic habitats, where NIR light-driven oxygenic photosynthesis may be significant. 相似文献
10.
Lars Behrendt Asker Brejnrod Martin Schliep S?ren J S?rensen Anthony WD Larkum Michael Kühl 《The ISME journal》2015,9(9):2108-2111
Chlorophyll (Chl) f is the most recently discovered chlorophyll and has only been found in cyanobacteria from wet environments. Although its structure and biophysical properties are resolved, the importance of Chl f as an accessory pigment in photosynthesis remains unresolved. We found Chl f in a cyanobacterium enriched from a cavernous environment and report the first example of Chl f-supported oxygenic photosynthesis in cyanobacteria from such habitats. Pigment extraction, hyperspectral microscopy and transmission electron microscopy demonstrated the presence of Chl a and f in unicellular cyanobacteria found in enrichment cultures. Amplicon sequencing indicated that all oxygenic phototrophs were related to KC1, a Chl f-containing cyanobacterium previously isolated from an aquatic environment. Microsensor measurements on aggregates demonstrated oxygenic photosynthesis at 742 nm and less efficient photosynthesis under 768- and 777-nm light probably because of diminished overlap with the absorption spectrum of Chl f and other far-red absorbing pigments. Our findings suggest the importance of Chl f-containing cyanobacteria in terrestrial habitats.The textbook concept that oxygenic phototrophs primarily use radiation in the visible range (400–700 nm) has been challenged by several findings of unique cyanobacteria and chlorophylls (Chl) over the past two decades (Miyashita et al., 1996; Chen et al., 2010; Croce and van Amerongen, 2014) Unicellular cyanobacteria in the genus Acaryochloris primarily employ Chl d for oxygenic photosynthesis at 700–720 nm (Miyashita et al., 1996) and thrive in shaded habitats with low levels of visible light but replete of near-infrared radiation (NIR, >700 nm, Kühl et al., 2005; Behrendt et al., 2011, 2012). Furthermore, Chl f was recently discovered in filamentous (Chen et al., 2010; Airs et al., 2014; Gan et al., 2014) and unicellular cyanobacteria (Miyashita et al., 2014), enabling light harvesting even further into the NIR region up to ∼740 nm, often aided by employing additional far-red light-absorbing pigments such as Chl d and phycobiliproteins (Gan et al., 2014). Whereas the biochemical structure (Willows et al., 2013) and biophysical properties (Li et al., 2013; Tomo et al., 2014) of Chl f have been studied in detail, the actual importance of this new chlorophyll for photosynthesis is hardly explored (Li et al., 2014).Chlorophyll f has been found in cyanobacteria originating from aquatic/wet environments: the filamentous Halomicronema hongdechloris from stromatolites in Australia (Chen et al., 2012), a unicellar morphotype (Strain KC1) from Lake Biwa in Japan (Akutsu et al., 2011; Miyashita et al., 2014) and a filamentous Leptolyngbya sp. strain (JSC-1, Gan et al., 2014) from a hot-spring and in a unicellular Chlorogloeopsis fritschii strain from rice paddies (Airs et al., 2014). In this study, we report on a unicellular Chl f-containing cyanobacterium originating from a wet cavernous habitat and demonstrate its capability of NIR-driven oxygenic photosynthesis. Enrichments of the new cyanobacterium were obtained from a dense dark green-blackish biofilm dominated by globular morphotypes of Nostocaceae growing on moist limestone outside Jenolan Caves, NSW, Australia. The sampling site was heavily shaded even during mid-day with low irradiance levels of 400- to 700-nm light varying from 0.5 to 5 μmol photons m−2 s−1. Biofilms were carefully scraped off the substratum and kept in shaded zip-lock bags in a moist atmosphere until further processing. Samples were then incubated at 28 °C in a f/2 medium under NIR at 720 nm (∼10 μmol photons m−2 s−1) yielding conspicuous green cell aggregates after several months of incubation. Repeated transfer of the aggregates into fresh medium resulted in a culture predominated by green cell clusters (Figure 1a), exhibiting orange-red fluorescence upon excitation with blue light (Figure 1b). Transmission electron microscopy revealed that the green clusters consisted of slightly elongated unicellular cyanobacteria (∼1- to 2-μm wide and ∼2- to 3-μm long), with stacked thylakoids and embedded in a joint polymer matrix (Figure 1c). Hyperspectral microscopy (Kühl and Polerecky, 2008) of the clusters revealed distinct troughs in the transmission spectra at absorption maxima indicative of Chl a (675–680 nm) and Chl f (∼720 nm; Figure 1d, red line). In situ spectral irradiance measurements at the sampling site showed strong depletion of visible wavelengths in the 480- to 710-nm range (Figure 1d, gray line), whereas highest light levels were found in the near-infrared region of the solar spectrum at 710–900 nm. The presence of Chl a and f was further confirmed in enrichment cultures using high-performance liquid chromatography-based pigment analysis (Figure 1e, Supplementary Figure S1), while no Chl d was detected. In addition, weak spectral signatures of carotenoids and phycobilins, with absorption occurring at ∼495 and 665 nm, were evident in the hyperspectral data. Cyanobacteria, including those producing Chl d/f, are known to actively remodel their pigment content in response to the available light spectrum (Stomp et al., 2007; Chen and Scheer, 2013; Gan et al., 2014) and Chl d/f has almost exclusively been found in cyanobacteria grown under far-red light and not under visible light (Kühl et al., 2005; Chen et al., 2010; Airs et al., 2014; Gan et al., 2014; Li et al., 2014; Miyashita et al., 2014). Recent work describes this acclimation response as ‘Far-Red Light photoacclimation'' (FaRLiP), which, in strain JSC-1, comprises a global change in gene expression and structural remodeling of the PSII/PSI core proteins and phycobilisome constituents (Gan et al., 2014). The extent to which this arrangement results in optimized photosynthetic performance is only known for the NIR (=710 nm)-acclimated strain JSC-1, where exposure to wavelengths >695 nm resulted in 40% higher O2 evolution rates as compared with cells that were previously adapted to red light (645 nm; Gan et al., 2014). Yet the discrimination of actinic wavelengths and their relative effect on gross photosynthesis in Chl f-containing cells needs further investigation. Using an O2 microsensor and the light–dark shift method (Revsbech et al., 1983) on embedded Chl f-containing aggregates, we found maximal gross photosynthesis rates (∼1.06 μmol O2 cm−3 s−1) to occur at irradiances of ∼250 μmol photons m−2 s−1 of 742 nm (half-bandwidth, HBW, 25 nm, Figures 2a and b) with light saturation to occur very early at ∼35 μmol photons m−2 s−1. Further red-shifted actinic light, that is, 768 nm (HBW 28 nm) and 777 nm (HBW 30 nm), yielded lower O2 evolution rates, which, in all likelihood, are an effect of the diminished overlap with far-red light-absorbing pigments, including Chl f (Figures 2a and b). As O2 evolution rates were measured on non-axenic cell aggregates, 16S rDNA amplicon sequencing was employed to determine the microbial diversity found within the enrichment culture. This revealed the presence of a variety of bacterial types, including anoxygenic phototrophs, yet all sequences for known oxygenic phototrophs in the data set (∼9.3% of all reads on the order level, Supplementary Figure S2) formed a single operational taxonomic unit (OTU) closely affiliated with the Chl f-containing strain KC1 (Miyashita et al., 2014, Figure 2c).Open in a separate windowFigure 1Imaging and pigment analysis of Chl f-containing cyanobacteria isolated from a cavernous low-light environment. (a) Representative bright field microscope image of cultured cells grown under 720 nm NIR. (b) Fluorescence image of the same cells as in a, excited at 450–490 nm, with emission being detected at >510 nm. (c) Transmission electron microscopy of a Chl f-containing cyanobacterium with densely stacked thylakoid membranes. (d) Transmittance spectrum of cell aggregate determined by hyperspectral imaging (red line). Ambient light conditions at the site of isolation (gray line), as measured by a spectroradiometer. Note the Chl f-specific in vivo absorption at ∼720 nm in the transmittance spectrum (dotted line). Small insert picture denotes the cells and area of interest (black arrow) from which the spectrum was taken. (e) In vitro absorption spectrum of Chl f extracted from enrichment cultures and analyzed via high-performance liquid chromatography. The two Chl f-specific absorption peaks (404 and 704 nm in acetone:MeOH solvent) are indicated.Open in a separate windowFigure 2Taxonomic affiliation and O2 evolution of Chl f-containing cells as determined by O2 microelectrode measurements and 16 S rDNA amplicon sequencing. (a) Emission spectra of narrow-band light-emitting diodes (LEDs) used in this study, with peak emissions at 742, 768 and 777 nm indicated by a–c, respectively. (b) Gross photosynthesis measured via an O2 microsensor placed in a clump of agarose-embedded Chl f-containing cells. Different NIR irradiance was administered by the LEDs in a and by altering the distance of the LEDs to the embedded cells. (c) Phylogenetic affiliation of known Chl f and/or Chl d-containing cyanobacteria (highlighted in gray) and their respective habitat/place of isolation. Taxonomy was determined by clustering all known oxygenic phototrophs found in enrichment cultures from this study (at order level) into a single OTU (=292 bp length, see Supplementary Materials for details). Phylogeny was inferred using Maximum-likelihood in conjunction with the GTR +I +G nucleotide substitution model, tree stability was tested using bootstrapping with 100 replicates. The analysis involved 39 nucleotide sequences each truncated to a length of 292 bp. Here, the green-sulphur bacterium Chlorobium tepidum TLS was chosen as the outgroup.This advocates that cells from our enrichment culture are related to KC1 cells and supports, in conjunction with further morphological-, physiological- and ultrastructural evidence, that Chl f is extending the usable light spectrum for oxygenic photosynthesis in a cavernous low-light environment. Given the lifestyle and known habitats of recognized Chl d/f-producing cyanobacteria (Figure 2c), we propose that many, if not all, surface-associated cyanobacteria are intrinsically capable of producing far-red light-absorbing pigments and to actively employ them in oxygenic photosynthesis as a result of FaRLiP or similar, yet unknown, mechanisms. 相似文献