57 research outputs found
Same but different â pseudo-pectin in the charophytic alga Chlorokybus atmophyticus
All landâplant cell walls possess hemicelluloses, cellulose and anionic pectin. The walls of their cousins, the charophytic algae, exhibit some similarities to land plantsâ but also major differences. Charophyte âpectinsâ are extractable by conventional landâplant methods, although they differ significantly in composition. Here, we explore âpectinsâ of an earlyâdiverging charophyte, Chlorokybus atmophyticus, characterising the anionic polysaccharides that may be comparable to âpectinsâ in other streptophytes. Chlorokybus âpectinâ was anionic and upon acid hydrolysis gave GlcA, GalA and sulphate, plus neutral sugars (AraâGlc>Gal>Xyl); Rha was undetectable. Most Gal was the lâenantiomer. A relatively acidâresistant disaccharide was characterised as ÎČâdâGlcAâ(1â4)âlâGal. Two Chlorokybus âpectinâ fractions, separable by anionâexchange chromatography, had similar sugar compositions but different sulphateâester contents. No sugars were released from Chlorokybus âpectinâ by several endoâhydrolases [(1,5)âαâlâarabinanase, (1,4)âÎČâdâgalactanase, (1,4)âÎČâdâxylanase, endoâpolygalacturonase] and exoâhydrolases [αâ and ÎČâdâgalactosidases, αâ(1,6)âdâxylosidase]. âDriselaseâ, which hydrolyses most landâplant cell wall polysaccharides to monoâ and disaccharides, released no sugars except traces of starchâderived Glc. Thus, the Ara, Gal, Xyl and GalA of Chlorokybus âpectinâ were not nonâreducing termini with configurations familiar from landâplant polysaccharides (αâlâAraf, αâ and ÎČâdâGalp, αâ and ÎČâdâXylp and αâdâGalpA), nor midâchain residues of αâ(1â5)âlâarabinan, ÎČâ(1â4)âdâgalactan, ÎČâ(1â4)âdâxylan or αâ(1â4)âdâgalacturonan. In conclusion, Chlorokybus possesses anionic âpecticâ polysaccharides, possibly fulfilling pectic roles but differing fundamentally from landâplant pectin. Thus, the evolution of landâplant pectin since the last common ancestor of Chlorokybus and land plants is a long and meandering path involving loss of sulphate, most lâGal and most dâGlcA; reâconfiguration of Ara, Xyl and GalA; and gain of Rha
Di-isodityrosine, a novel tetrametric derivative of tyrosine in plant cell wall proteins: a new potential cross-link
Montbresides AâD:Antibacterial p-coumaroyl esters of a new sucrose-based tetrasaccharide from Crocosmia Ă crocosmiiflora (montbretia) flowers
The pectic disaccharides lepidimoic acid and ÎČ-d-xylopyranosyl-(1â3)-d-galacturonic acid occur in cress-seed exudate but lack allelochemical activity
Background and aims Cress-seed (Lepidium sativum) exudate exerts an allelochemical effect, promoting excessive hypocotyl elongation and inhibiting root growth in neighbouring Amaranthus caudatus seedlings. We investigated acidic disaccharides present in cress-seed exudate, testing the proposal that the allelochemical is an oligosaccharinâlepidimoic acid (LMA; 4-deoxy-ÎČ-l-threo-hex-4-enopyranuronosyl-(1â2)-l-rhamnose). Methods Cress-seed exudate was variously treated [heating, ethanolic precipitation, solvent partitioning, high-voltage paper electrophoresis and gel-permeation chromatography (GPC)], and the products were bioassayed for effects on dark-grown Amaranthus seedlings. Two acidic disaccharides, including LMA, were isolated and characterized by electrophoresis, thin-layer chromatography (TLC) and nuclear magnetic resonance (NMR) spectroscopy, and then bioassayed. Key Results Cress-seed exudate contained low-M(r), hydrophilic, heat-stable material that strongly promoted Amaranthus hypocotyl elongation and inhibited root growth, but that separated from LMA on electrophoresis and GPC. Cress-seed exudate contained âŒ250â”m LMA, whose TLC and electrophoretic mobilities, susceptibility to mild acid hydrolysis and NMR spectra are reported. A second acidic disaccharide, present at âŒ120â”m, was similarly characterized, and shown to be ÎČ-d-xylopyranosyl-(1â3)-d-galacturonic acid (XylâGalA), a repeat unit of xylogalacturonan. Purified LMA and XylâGalA when applied at 360 and 740â”m, respectively, only slightly promoted Amaranthus hypocotyl growth, but equally promoted root growth and thus had no effect on the hypocotyl:root ratio, unlike total cress-seed exudate. Conclusions LMA is present in cress seeds, probably formed by rhamnogalacturonan lyase action on rhamnogalacturonan-I during seed development. Our results contradict the hypothesis that LMA is a cress allelochemical that appreciably perturbs the growth of potentially competing seedlings. Since LMA and XylâGalA slightly promoted both hypocotyl and root elongation, their effect could be nutritional. We conclude that rhamnogalacturonan-I and xylogalacturonan (pectin domains) are not sources of oligosaccharins with allelochemical activity, and the biological roles (if any) of the disaccharides derived from them are unknown. The main allelochemical principle in cress-seed exudate remains to be identified
Organometallic iridium(III) anticancer complexes with new mechanisms of action: NCI-60 screening, mitochondrial targeting, and apoptosis
Platinum complexes related to cisplatin, cis-[PtCl2(NH3)2], are successful anticancer drugs; however, other transition metal complexes offer potential for combating cisplatin resistance, decreasing side effects, and widening the spectrum of activity. Organometallic half-sandwich iridium (IrIII) complexes [Ir(Cpx)(XY)Cl]+/0 (Cpx = biphenyltetramethylcyclopentadienyl and XY = phenanthroline (1), bipyridine (2), or phenylpyridine (3)) all hydrolyze rapidly, forming monofunctional G adducts on DNA with additional intercalation of the phenyl substituents on the Cpx ring. In comparison, highly potent complex 4 (Cpx = phenyltetramethylcyclopentadienyl and XY = N,N-dimethylphenylazopyridine) does not hydrolyze. All show higher potency toward A2780 human ovarian cancer cells compared to cisplatin, with 1, 3, and 4 also demonstrating higher potency in the National Cancer Institute (NCI) NCI-60 cell-line screen. Use of the NCI COMPARE algorithm (which predicts mechanisms of action (MoAs) for emerging anticancer compounds by correlating NCI-60 patterns of sensitivity) shows that the MoA of these IrIII complexes has no correlation to cisplatin (or oxaliplatin), with 3 and 4 emerging as particularly novel compounds. Those findings by COMPARE were experimentally probed by transmission electron microscopy (TEM) of A2780 cells exposed to 1, showing mitochondrial swelling and activation of apoptosis after 24 h. Significant changes in mitochondrial membrane polarization were detected by flow cytometry, and the potency of the complexes was enhanced ca. 5Ă by co-administration with a low concentration (5 ÎŒM) of the Îł-glutamyl cysteine synthetase inhibitor L-buthionine sulfoximine (L-BSO). These studies reveal potential polypharmacology of organometallic IrIII complexes, with MoA and cell selectivity governed by structural changes in the chelating ligands
The HIPASS Catalogue - II. Completeness, Reliability, and Parameter Accuracy
The HI Parkes All Sky Survey (HIPASS) is a blind extragalactic HI 21-cm
emission line survey covering the whole southern sky from declination -90 to
+25. The HIPASS catalogue (HICAT), containing 4315 HI-selected galaxies from
the region south of declination +2, is presented in Meyer et al. (2004a, Paper
I). This paper describes in detail the completeness and reliability of HICAT,
which are calculated from the recovery rate of synthetic sources and follow-up
observations, respectively. HICAT is found to be 99 per cent complete at a peak
flux of 84 mJy and an integrated flux of 9.4 Jy km/s. The overall reliability
is 95 per cent, but rises to 99 per cent for sources with peak fluxes >58 mJy
or integrated flux > 8.2 Jy km/s. Expressions are derived for the uncertainties
on the most important HICAT parameters: peak flux, integrated flux, velocity
width, and recessional velocity. The errors on HICAT parameters are dominated
by the noise in the HIPASS data, rather than by the parametrization procedure.Comment: Accepted for publication in MNRAS. 12 pages, 11 figures. Paper with
higher resolution figures can be downloaded from http://hipass.aus-vo.or
Biogenic metallic elements in the human brain?
The chemistry of copper and iron plays a critical role in normal brain function. A variety of enzymes and proteins containing positively charged Cu+, Cu2+, Fe2+, and Fe3+ control key processes, catalyzing oxidative metabolism and neurotransmitter and neuropeptide production. Here, we report the discovery of elemental (zeroâoxidation state) metallic Cu0 accompanying ferromagnetic elemental Fe0 in the human brain. These nanoscale biometal deposits were identified within amyloid plaque cores isolated from Alzheimerâs disease subjects, using synchrotron x-ray spectromicroscopy. The surfaces of nanodeposits of metallic copper and iron are highly reactive, with distinctly different chemical and magnetic properties from their predominant oxide counterparts. The discovery of metals in their elemental form in the brain raises new questions regarding their generation and their role in neurochemistry, neurobiology, and the etiology of neurodegenerative disease
Collision, Collusion and Coincidence: Pop Artâs Fairground Parallel
This article looks at parallel methods, motivations and modes of consumption between formative British pop art and British fairground art. I focus on two strands, the emergent critical work of the Independent Group and the school of artists based at the Royal College of Art under the nominal leadership of Peter Blake. I use iconographical and iconological methods to compare the content of the art, and then examine how pop art tried to create both a critical and playful distancing from established rules and practices of the artistic canon. I focus on non-institutional cultural groupings and diffuse production and consumption models
Recommended from our members
Snowball Earth climate dynamics and Cryogenian geology-geobiology
Geological evidence indicates that grounded ice sheets reached sea level at all latitudes during two long-lived Cryogenian (58 and â„5 My) glaciations. Combined uranium-lead and rhenium-osmium dating suggests that the older (Sturtian) glacial onset and both terminations were globally synchronous. Geochemical data imply that CO2 was 102 PAL (present atmospheric level) at the younger termination, consistent with a global ice cover. Sturtian glaciation followed breakup of a tropical supercontinent, and its onset coincided with the equatorial emplacement of a large igneous province. Modeling shows that the small thermal inertia of a globally frozen surface reverses the annual mean tropical atmospheric circulation, producing an equatorial desert and net snow and frost accumulation elsewhere. Oceanic ice thickens, forming a sea glacier that flows gravitationally toward the equator, sustained by the hydrologic cycle and by basal freezing and melting. Tropical ice sheets flow faster as CO2 rises but lose mass and become sensitive to orbital changes. Equatorial dust accumulation engenders supraglacial oligotrophic meltwater ecosystems, favorable for cyanobacteria and certain eukaryotes. Meltwater flushing through cracks enables organic burial and submarine deposition of airborne volcanic ash. The subglacial ocean is turbulent and well mixed, in response to geothermal heating and heat loss through the ice cover, increasing with latitude. Terminal carbonate deposits, unique to Cryogenian glaciations, are products of intense weathering and ocean stratification. Whole-ocean warming and collapsing peripheral bulges allow marine coastal flooding to continue long after ice-sheet disappearance. The evolutionary legacy of Snowball Earth is perceptible in fossils and living organisms
A resource-advantage perspective on the orchestration of ambidexterity
This is an Accepted Manuscript of an article published by Taylor & Francis in Service Industries Journal on 31 Jul 2014, available online: http://dx.doi.org/10.1080/02642069.2014.942655Strategic resources are key inputs to strategy that can form the basis of superior service performance, yet there is scarce research on the strategic resources used by managers to realise ambidexterity: the simultaneous pursuit of alignment and adaptability. In this article, we draw on a qualitative case study of a leading European airline and examine the resource bundles used by managers in their orchestration of ambidexterity. Adopting a resource-advantage perspective, the study illustrates elements of human, organisational, and informational capital that are mobilised by managers in their incorporation of alignment-oriented and adaptability-oriented activities. By moving beyond a linear association between strategic resources and ambidextrous organisations, we argue that managers' orchestration of ambidexterity is central to how service organisations manage their strategic resources and enhance competitiveness. Overall, we highlight the micro managerial level as an important point of observation to extend current thinking on the âhowâ of ambidexterity in service organisations
- âŠ