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Abstract. Woodland colonization on wetlands is considered to have a detrimental effect on their ecological value, even though detailed analysis of this process is lacking. This paper provides an evaluation of the ecological changes resulting from succession of poor fen (base‐poor mire) to willow wet woodland on Goss Moor NNR in Cornwall, UK. Different ages of willow carr were associated with eight understorey communities. During willow colonization, in the ground flora, there was a progressive decrease in poor fen species and an associated increase in woodland species, which appeared to be related to an increase in canopy cover and therefore shade. The most diverse community was found to be the most recent willow and was dominated by poor fen species. The oldest willow was the second most diverse and was associated with a reduction in poor fen species and an increase in woodland species. Architectural features were used successfully to assess the general condition and structure of willow. Tree height and DBH were identified as useful parameters to accurately assess willow age in the field. The implications of active intervention to remove willow in order to conserve the full range of communities within the hydrosere are discussed. 相似文献
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Initiation of DNA replication of the papillomavirus genome is a multi-step process involving the sequential loading of viral E1 protein subunits onto the origin of replication. Here we have captured structural snapshots of two sequential steps in the assembly process. Initially, an E1 dimer binds to adjacent major grooves on one face of the double helix; a second dimer then binds to another face of the helix. Each E1 monomer has two DNA-binding modules: a DNA-binding loop, which binds to one DNA strand and a DNA-binding helix, which binds to the opposite strand. The nature of DNA binding suggests a mechanism for the transition between double- and single-stranded DNA binding that is implicit in the progression to a functional helicase. 相似文献
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Trevor D. Rapson Andrei V. Astashkin Kayunta Johnson-Winters Paul V. Bernhardt Ulrike Kappler Arnold M. Raitsimring John H. Enemark 《Journal of biological inorganic chemistry》2010,15(4):505-514
Continuous-wave and pulsed electron paramagnetic resonance (EPR) spectroscopy have been used to characterize two variants
of bacterial sulfite dehydrogenase (SDH) from Starkeya novella in which the conserved active-site arginine residue (R55) is replaced by a neutral amino acid residue. Substitution by the
hydrophobic methionine residue (SDHR55M) has essentially no effect on the pH dependence of the EPR properties of the Mo(V) center, even though the X-ray structure
of this variant shows that the methionine residue is rotated away from the Mo center and a sulfate anion is present in the
active-site pocket (Bailey et al. in J Biol Chem 284:2053–2063, 2009). For SDHR55M only the high-pH form is observed, and samples prepared in H2
17O-enriched buffer show essentially the same 17O hyperfine interaction and nuclear quadrupole interaction parameters as SDHWT enzyme. However, the pH dependence of the EPR spectra of SDHR55Q, in which the positively charged arginine is replaced by the neutral hydrophilic glutamine, differs significantly from that
of SDHWT. For SDHR55Q the blocked form with bound sulfate is generated at low pH, as verified by 33S couplings observed upon reduction with 33S-labeled sulfite. This observation of bound sulfate for SDHR55Q supports our previous hypothesis that sulfite-oxidizing enzymes can exhibit multiple pathways for electron transfer and product
release (Emesh et al. in Biochemistry 48:2156–2163, 2009). At pH ≥ 8 the high-pH form dominates for SDHR55Q. 相似文献
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Annemarie MM Vlaar Angela EP Bouwmans Marinus JPG van Kroonenburgh Werner H Mess Selma C Tromp Piet GWM Wuisman Alfons GH Kessels Ania Winogrodzka Wim EJ Weber 《BMC neurology》2007,7(1):28
Background
Parkinson's disease (PD) is the second most common neurodegenerative disorder. As there is no definitive diagnostic test, its diagnosis is based on clinical criteria. Recently transcranial duplex scanning (TCD) of the substantia nigra in the brainstem has been proposed as an instrument to diagnose PD. We and others have found that TCD scanning of substantia nigra duplex is a relatively accurate diagnostic instrument in patients with parkinsonian symptoms. However, all studies on TCD so far have involved well-defined, later-stage PD patients, which will obviously lead to an overestimate of the diagnostic accuracy of TCD. 相似文献7.
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Raitsimring AM Astashkin AV Feng C Wilson HL Rajagopalan KV Enemark JH 《Inorganica chimica acta》2008,361(4):941-946
The Mo(V) forms of the Tyr343Phe (Y343F) mutant of human sulfite oxidase (SO) have been investigated by continuous wave (CW) and variable frequency pulsed EPR spectroscopies as a function of pH. The CW EPR spectrum recorded at low-pH (∼6.9) has g-values similar to those known for the low-pH form of the native vertebrate SO (original lpH form); however, unlike the spectrum of original lpH SO, it does not show any hyperfine splittings from a nearby exchangeable proton. The detailed electron spin echo (ESE) envelope modulation (ESEEM) and pulsed electron-nuclear double resonance (ENDOR) experiments also did not reveal any nearby protons that could belong to an exchangeable ligand at the molybdenum center. These results suggest that under low-pH conditions the active site of Y343F SO is in the “blocked” form, with the Mo(V) center coordinated by sulfate. With increasing pH the EPR signal from the “blocked” form decreases, while a signal similar to that of the original lpH form appears and becomes the dominant signal at pH >9. In addition, both the CW EPR and ESE-detected field-sweep spectra reveal a considerable contribution from a signal similar to that usually detected for the high-pH form of native vertebrate SO (original hpH form). The nearby exchangeable protons in both of the component forms observed at high-pH were studied by the ESEEM spectroscopy. These results indicate that the Y343F mutation increases the apparent pKa of the transition from the lpH to hpH forms by ∼2 pH units. 相似文献