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971.
Ping L Büchler R Mithöfer A Svatos A Spiteller D Dettner K Gmeiner S Piel J Schlott B Boland W 《Environmental microbiology》2007,9(6):1572-1583
A novel type of a microbial N-acyl amino acid hydrolase (AAH) from insect gut bacteria was purified, cloned and functionally characterized. The enzyme was obtained from Microbacterium arborescens SE14 isolated from the foregut of larvae of the generalist herbivore Spodoptera exigua. The substrates of AAH are N-acyl-glutamines previously reported to elicit plant defence reactions after introduction into the leaf during feeding. The isolated AAH catalyses the hydrolysis of the amide bond (K(m) = 36 micromol l(-1)) and, less efficient, the formation (K(m) = 3 mmol l(-1)) of the elicitor active N-acyl amino acids. The AAH from M. arborescens SE14 shows no homology to known fatty acyl amidases (EC 3.5.1.4) but belongs to the family of Dps proteins (DNA-binding protein from starved cell). In line with other DPS proteins AAH is a homododecamer (monomer 17 181 Da) and contains iron atoms (c. 1-16 iron atoms per subunit). Unlike genuine DPS proteins the enzyme does not significantly bind DNA. Amino acid hydrolase is the first member of the DPS family that catalyses the cleavage or formation of amide bonds. The participation of a microbial enzyme in the homeostasis of N-acyl-glutamines in the insect gut adds further complexity to the interaction between plants and their herbivores. 相似文献
972.
TRPM6 and TRPM7--Gatekeepers of human magnesium metabolism 总被引:5,自引:0,他引:5
Schlingmann KP Waldegger S Konrad M Chubanov V Gudermann T 《Biochimica et biophysica acta》2007,1772(8):813-821
Human magnesium homeostasis primarily depends on the balance between intestinal absorption and renal excretion. Magnesium transport processes in both organ systems - next to passive paracellular magnesium flux - involve active transcellular magnesium transport consisting of an apical uptake into the epithelial cell and a basolateral extrusion into the interstitium. Whereas the mechanism of basolateral magnesium extrusion remains unknown, recent molecular genetic studies in patients with hereditary hypomagnesemia helped gain insight into the molecular nature of apical magnesium entry into intestinal brush border and renal tubular epithelial cells. Patients with Hypomagnesemia with Secondary Hypocalcemia (HSH), a primary defect in intestinal magnesium absorption, were found to carry mutations in TRPM6, a member of the melastatin-related subfamily of transient receptor potential (TRP) ion channels. Before, a close homologue of TRPM6, TRPM7, had been characterized as a magnesium and calcium permeable ion channel vital for cellular magnesium homeostasis. Both proteins share the unique feature of an ion channel fused to a kinase domain with homology to the family of atypical alpha kinases. The aim of this review is to summarize the data emerging from clinical and molecular genetic studies as well as from electrophysiologic and biochemical studies on these fascinating two new proteins and their role in human magnesium metabolism. 相似文献
973.
974.
Matthias Finkbeiner Konrad Saur Peter Eyerer Yasunari Matsuno Atsushi Inaba 《The International Journal of Life Cycle Assessment》1999,4(3):127-132
Sustainable development can only be achieved if industry adoptsboth product related and organisation related environmental management tools, such as Life Cycle Assessment (LCA) and Environmental
Management Systems (EMS). In Japan, EMS (ISO 14001) is more widely applied than LCA (ISO 14040). Therefore,one means by which Japanese industries could be motivated to adopt and use LCA is to relate LCA-activities to the policies and
instruments of ISO 14001. The potential of such a comprehensive approach was analysed by a survey of 270 Japanese enterprises
(response rate 45%). The results indicate that 19% of the responding representatives had responsibilities for both LCA and
EMS, while the remaining only work in one of both fields. A statement in the company’s/ plant’s Environmental Policy of ISO
14001, stating that LCA is to be used as part of the EMS, was found in 42% of all companies. A surprising number (39%) either
already use, or plan to use, LCA and EMS as combinated/integrated tools. A strong argument for the establishment of a comprehensive
approach can be seen in the perception of the usefulness of LCA, which was rated significantly higher in companies that acknowledged
the complementary potential of LCA and EMS. 相似文献
975.
Michael F. Jobling Leanne R. Stewart Anthony R. White Catriona McLean Anna Friedhuber Fran Maher Konrad Beyreuther Colin L. Masters Colin J. Barrow Steven J. Collins Roberto Cappai 《Journal of neurochemistry》1999,73(4):1557-1565
The neurodegeneration seen in spongiform encephalopathies is believed to be mediated by protease-resistant forms of the prion protein (PrP). A peptide encompassing residues 106-126 of human PrP has been shown to be neurotoxic in vitro. The neurotoxicity of PrP106-126 appears to be dependent upon its adoption of an aggregated fibril structure. To examine the role of the hydrophobic core, AGAAAAGA, on PrP106-126 toxicity, we performed structure-activity analyses by substituting two or more hydrophobic residues for the hydrophilic serine residue to decrease its hydrophobicity. A peptide with a deleted alanine was also synthesized. We found all the peptides except the deletion mutant were no longer toxic on mouse cerebellar neuronal cultures. Circular dichroism analysis showed that the nontoxic PrP peptides had a marked decrease in beta-sheet structure. In addition, the mutants had alterations in aggregability as measured by turbidity, Congo red binding, and fibril staining using electron microscopy. These data show that the hydrophobic core sequence is important for PrP106-126 toxicity probably by influencing its assembly into a neurotoxic structure. The hydrophobic sequence may similarly affect aggregation and toxicity observed in prion diseases. 相似文献
976.
977.
Timothy G. Williamson †Victor Nurcombe ‡Konrad Beyreuther Colin L. Masters David H. Small 《Journal of neurochemistry》1995,65(5):2201-2208
Abstract: The binding of the amyloid protein precursor (APP) to heparan sulfate proteoglycans has been shown to stimulate the neurite-promoting activity of APP. In this study, proteoglycans that bind with high affinity to APP were characterized. Conditioned medium from cultures of postnatal day 3 mouse brain cells was applied to an affinity column containing a peptide homologous to a heparin-binding domain of APP. A fraction 17-fold enriched in proteoglycans was recovered by elution with a salt gradient. APP bound saturably and with high affinity to the affinity-purified proteoglycan fraction. Scatchard analysis of the binding showed that APP bound to high- and low-affinity sites with equilibrium dissociation constants of 1.4 × 10−11 and 6.5 × 10−10 M , respectively. APP, in conjunction with the affinity-purified proteoglycan fraction, promoted neurite outgrowth. The affinity-purified proteoglycan fraction contained a heparan sulfate proteoglycan and a chondroitin sulfate proteoglycan. Digestion of the affinity-purified fraction with heparitinase I revealed a core protein of 63–69-kDa molecular mass, whereas digestion with chondroitinase ABC revealed a core protein of 100–110 kDa. The results suggest that expression of specific APP-binding proteoglycans may be an important step in the regulation of the neurite outgrowth-promoting activity of APP. 相似文献
978.
Solidago canadensis is an invasive species from North America that is spreading across Europe, Australia and temperate Asia. We hypothesized that the species' wide ecological amplitude is also based on its potential in hydraulic acclimation, and analyzed hydraulic and anatomical properties along a transect with decreasing soil humidity. Stem hydraulic conductivity, vulnerability to drought‐induced embolism, stomatal closure during dehydration and xylem‐anatomical parameters were quantified at three sites. At the humid site, specific hydraulic conductivity of stems (1.0 ± 0.2 kg m–1 MPa–1 s–1) was about twofold higher, and leaf‐specific conductivity about 1.5 times higher (3.1 ± 0.5 kg m–1 MPa–1 s–1) than at the dry site. Water potential (Ψ) at 50% loss of conductivity was ?3.7 ± 0.1 MPa at the dry site and ?3.1 ± 0.2 MPa at the humid site (September). Vulnerability to drought‐induced embolism decreased along the transect and over the vegetation period. At drier sites, stomata started closing at lower Ψ while complete stomatal closure was reached at less negative Ψ (12% of maximum stomatal conductance: –2.5 ± 0.0 and ?3.0 ± 0.2 MPa at the dry and humid site). The safety margin between stomatal closure and 50% loss of conductivity was 1.2 and 0.2 MPa at the dry and humid sites. The observed variability indicated an efficient acclimation in hydraulic conductivity and safety: plants at dry sites exhibited lower specific hydraulic conductivity, higher embolism resistance and broader safety margins, signifying a trade‐off between the hydraulic safety and efficiency. The observed intraspecific plasticity in hydraulic and anatomical traits may help to explain the invasive potential of this species. 相似文献
979.
Harald Kosegarten Franz Grolig Andreas Esch Karl-Heinz Glüsenkamp Konrad Mengel 《Planta》1999,209(4):444-452
A fluorimetric ratio technique was elaborated to measure apoplastic pH in the outer root cortex of maize (Zea mays L.) grown hydroponically. A newly synthesized fluorescent probe, fluorescein boronic acid (pKa = 5.48), which covalently binds to the cell wall of the outer cell layers, was used. Under conditions of saturating ion concentrations
the apoplastic pH was determined along the root axis ranging from 1 to 30 mm behind the root tip. Apoplastic pH was recorded
for root segment areas (1 mm2), and pH values of high statistical significance were obtained. With an external solution of pH 5, the apoplastic pH was
about pH 5.1 in the division zone, between pH 4.8 and 4.9 in the elongation region and about pH 4.9 in the root hair zone.
At an external pH of 8.6, the difference between the external pH and the apoplastic pH was considerably more, with a pH of
5.2–5.3 in all root zones. Addition of 1 mM NH4
+ caused a small apoplastic pH decrease (0.05 of a pH unit) in all root zones. Apoplastic alkalization upon application of
6 mM NO3
− was highest (0.3 of a pH unit) in the zone where root hairs emerge; in the division and early elongation zones, apoplastic
pH increased only transiently. In the presence of 10 mM HCO3
−, NO3
− elicited a higher and persistent alkalization (0.06–0.25 of a pH unit) in all root zones. Application of fusicoccin reduced
apoplastic pH from 4.85 to 4.75 in the elongation zone, while inhibition of the H+-ATPase with vanadate alkalized the apoplast in the root hair zone from pH 5.4 to 5.6. The observed pH differences along the
root axis upon differential N supply and application of HCO3
− provide evidence that this new pH technique is a useful tool with which to measure apoplastic pH, and in future may permit
measurements at microsites at the cell level by use of microscope imaging.
Received: 26 August 1998 / Accepted: 4 May 1999 相似文献
980.
The generation of adult animals by nuclear cloning from adult donor cells is extremely inefficient, with most clones dying soon after implantation. In contrast, cloning from embryonic stem cell donor nuclei is significanty more efficient than from adult donor cells. However, regardless of donor cell type, all clones that survive to birth and beyond suffer serious phenotypic and gene expression abnormalities. All available evidence is consistent with the notion that the anomalous phenotypes of cloned animals are caused by faulty epigenetic reprogramming of the donor nucleus. Faulty reprogramming appears to be caused by the cloning process itself as well as by the epigenetic state of the donor nucleus. In contrast to reproductive cloning, faulty reprogramming of the donor nucleus does not tend to interfere with the application of nuclear transfer technology for therapeutic purposes (therapeutic cloning). 相似文献