bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cobalamin‐Dependent and Cobalamin‐Independent Methionine Synthases: Are There Two Solutions to the Same Chemical Problem?
Authors: Matthews Rowena G. , Smith April E. , Zhou Zhaohui S. , Taurog Rebecca E. , Bandarian Vahe , Evans John C. , Ludwig Martha 
Published: December 2003

AbstractTwo enzymes in Escherichia coli, cobalamin‐independent methionine synthase (MetE) and cobalamin‐dependent methionine synthase (MetH), catalyze the conversion of homocysteine (Hcy) to methionine using N(5)‐methyltetrahydrofolate (CH3‐H4folate) as the Me donor. Despite the absence of sequence homology, these enzymes employ very similar catalytic strategies. In each case, the pKa for the SH group of Hcy is lowered by coordination to Zn2+, which increases the concentration of the reactive thiolate at neutral pH. In each case, activation of CH3‐H4folate appears to involve protonation at N(5). CH3‐H4folate remains unprotonated in binary E⋅CH3‐H4folate complexes, and protonation occurs only in the ternary E⋅CH3‐H4folate⋅Hcy complex in MetE, or in the ternary E⋅CH3‐H4folate⋅cob(I)alamin complex in MetH. Surprisingly, the similarities are proposed to extend to the structures of these two unrelated enzymes. The structure of a homologue of the Hcy‐binding region of MetH, betainehomocysteine methyltransferase, has been determined. A search of the three‐dimensional‐structure data base by means of the structure‐comparison program DALI indicates similarity of the BHMT structure with that of uroporphyrin decarboxylase (UroD), a homologue of the MT2‐A and MT2‐M proteins from Archaea, which catalyze Me transfers from methylcorrinoids to coenzyme M and share the Zn‐binding scaffold of MetE. Here, we present a model for the Zn binding site of MetE, obtained by grafting the Zn ligands of MT2‐A onto the structure of UroD.
Synthesis of Selectively 15N‐Labeled 2′‐O‐{[(Triisopropylsilyl)oxy]methyl}(=tom)‐Protected Ribonucleoside Phosphoramidites and Their Incorporation into a Bistable 32Mer RNA Sequence
Authors: Wenter Philipp , Pitsch Stefan 
Published: December 2003

AbstractWe present optimized reaction conditions for the conversion of 2′‐O‐{[(triisopropylsilyl)oxy]methyl}(=tom) protected uridine and adenosine nucleosides into the corresponding protected (3‐15N)‐labeled uridine and cytidine and (1‐15N)‐labeled adenosine and guanosine nucleosides 4, 6, 12, and 18, respectively (Schemes 1–4). On a DNA synthesizer, the resulting 15N‐labeled 2′‐O‐tom‐protected phosphoramidite building blocks 19–22 were efficiently incorporated into five selected positions of a bistable 32mer RNA sequence 23 (known to adopt two different structures) (Fig. 1). By 2D‐HSQC and HNN‐COSY experiments in H2O/D2O 9 : 1, the 15N‐signals of all base‐paired 15N‐labeled nucleotides could be identified and attributed to one of the two coexisting structures of 23.
Automated Synthesis of Oligosaccharides
Authors: Palmacci Emma R. , Plante Obadiah J. , Hewitt Michael C. , Seeberger Peter H. 
Published: December 2003

AbstractThe chemical synthesis of oligosaccharides with an automated solid‐phase synthesizer is described. An octenediol linker served to attach the growing oligosaccharide chain to the solid support, and the desired structures were cleaved from the support via olefin metathesis to afford a pentenyl glycoside. The automated syntheses of several important carbohydrates, including a pentarhamnoside, a proteoglycan linkage‐region tetrasaccharide, a phytoalexin elicitor dodecasaccharide, and a branched Leishmania lipophosphoglycan tetrasaccharide, were accomplished in higher overall yield and ca. 20 times faster than with solution‐phase methods.
Stereocontrolled Synthesis of (2R,3S)‐2‐Methylisocitrate, a Central Intermediate in the Methylcitrate Cycle
Authors: Darley Dan J. , Selmer Thorsten , Clegg William , Harrington Ross W. , Buckel Wolfgang , Golding Bernard T. 
Published: December 2003

Abstract2‐Methylisocitrate (=3‐hydroxybutane‐1,2,3‐tricarboxylic acid) is an intermediate in the oxidation of propanoate to pyruvate (=2‐oxopropanoate) via the methylcitrate cycle in both bacteria and fungi (Scheme 1). Stereocontrolled syntheses of (2R,3S)‐ and (2S,3R)‐2‐methylisocitrate (98% e.e.) were achieved starting from (R)‐ and (S)‐lactic acid (=(2R)‐ and (2S)‐2‐hydroxypropanoic acid), respectively. The dispiroketal (6S,7S,15R)‐15‐methyl‐1,8,13,16‐tetraoxadispiro[5.0.5.4]hexadecan‐14‐one (2a) derived from (R)‐lactic acid was deprotonated with lithium diisopropylamide to give a carbanion that was condensed with diethyl fumarate (Scheme 3). The configuration of the adduct diethyl (2S)‐2‐[(6S,7S,14R)‐14‐methyl‐15‐oxo‐1,8,13,16‐tetraoxadispiro[5.0.5.4]hexadec‐14‐yl]butanedioate (3a) was assigned by consideration of possible transition states for the fumarate condensation (cf. Scheme 2), and this was confirmed by a crystal‐structure analysis. The adduct was subjected to acid hydrolysis to afford the lactone 4a of (2R,3S)‐2‐methylisocitrate and hence (2R,3S)‐2‐methylisocitrate. Similarly, (S)‐lactic acid led to (2S,3R)‐2‐methylisocitrate. Comparison of 2‐methylisocitrate produced enzymatically with the synthetic enantiomers established that the biologically active isomer is (2R,3S)‐2‐methylisocitrate.
Achiral Calcium‐Oxalate Crystals with Chiral Morphology from the Leaves of Some Solanacea Plants
Authors: Levy‐Lior Avital , Weiner Steve , Addadi Lia 
Published: December 2003

AbstractThe leaves of some plants, particularly among the Solanacea, contain crystals of calcium oxalate with a peculiar chiral pseudo‐tetrahedral morphology, even though the calcium oxalate crystal structure is centrosymmetric, hence achiral. We studied the morphology of these crystals extracted from the leaves of three Solanacea plants: the potato, the hot pepper, and a species of wild Solanum. The crystal morphology was the same in all three species. Based on the examination of more than 100 crystals from each plant, we showed that the crystal morphology is chiral with invariant chirality. We suggest that morphological chirality is induced by macromolecules during nucleation from a specific, genetically encoded crystal plane, and is further established during subsequent controlled crystal growth. This is one of few examples where it is possible to deduce a molecular mechanism for biologically induced breaking of morphological symmetry in organisms. A very high level of recognition is required by the macromolecules to allow them to distinguish between symmetry‐related crystal planes. It is also surprising that this finely controlled mechanism of crystal formation, including the chiral morphology, has been conserved during evolution.
Molecular Shape and Intermolecular Liaison: Hydrocarbons and Fluorocarbons
Authors: Dunitz Jack D. , Gavezzotti Angelo , Schweizer W. Bernd 
Published: December 2003

AbstractWhereas aliphatic hydrocarbon/fluorocarbon mixtures show mutual ‘phobicity’ (e.g., positive deviations from Raoult's Law), their aromatic counterparts show the opposite behavior. Hexafluorobenzene forms co‐crystals with many aromatic hydrocarbons, but co‐crystals are unknown in the aliphatic series. This remarkable contrast between the behaviors of aliphatic and aromatic hydrocarbon/fluorocarbon mixtures calls for explanation, and we attempt to provide one in terms of the difference in overall molecular shape – disk vs. cylinder – using the new PIXEL method for calculating intermolecular energies.
Peripheral nerve regeneration using acellular nerve grafts
Authors: Kim Byung‐Soo , Yoo James J. , Atala Anthony 
Published: December 2003

AbstractLong gap peripheral nerve injuries usually require a graft to facilitate axonal regeneration into the distal nerve stump. The use of autografts is often limited because of graft availability and donor‐site morbidity. We investigated whether acellular nerve allografts would provide an appropriate channel for the promotion and induction of sciatic nerve regeneration in rats. Axons sprouted from the proximal portion and reached the distal portion in the 1 cm‐long grafts by 1 month. The number of axons in the regenerated nerves was similar to that of normal nerves at 1 month. Loading the grafts with βNGF and VEGF increased the number and mean diameter of axons and neovascularization in the regenerated nerves at 1 month. The motor conduction velocity increased over time and reached 63 ± 10% of that of normal nerves at 6 months. The nerve injuries treated with the acellular grafts had a significant improvement in motor, nociception, and proprioception function compared to untreated nerves. The results from this study suggest that acellular nerve allografts may be a useful biomaterial for functional peripheral nerve regeneration. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 68A: 201–209, 2004
Attachment and spreading of fibroblasts on an RGD peptide–modified injectable hyaluronan hydrogel
Authors: Shu Xiao Zheng , Ghosh Kaustabh , Liu Yanchun , Palumbo Fabio S. , Luo Yi , Clark Richard A. , Prestwich Glenn D. 
Published: December 2003

AbstractHyaluronan (HA) hydrogels resist attachment and spreading of fibroblasts and most other mammalian cell types. A thiol‐modified HA (3,3′‐dithiobis(propanoic dihydrazide) [HA‐DTPH]) was modified with peptides containing the Arg‐Gly‐Asp (RGD) sequence and then crosslinked with polyethylene glycol (PEG) diacrylate (PEGDA) to create a biomaterial that supported cell attachment, spreading, and proliferation. The hydrogels were evaluated in vitro and in vivo in three assay systems. First, the behavior of human and murine fibroblasts on the surface of the hydrogels was evaluated. The concentration and structure of the RGD peptides and the length of the PEG spacer influenced cell attachment and spreading. Second, murine fibroblasts were seeded into HA‐DTPH solutions and encapsulated via in situ crosslinking with or without bound RGD peptides. Cells remained viable and proliferated within the hydrogel for 15 days in vitro. Although the RGD peptides significantly enhanced cell proliferation on the hydrogel surface, the cell proliferation inside the hydrogel in vitro was increased only modestly. Third, HA‐DTPH/PEGDA/peptide hydrogels were evaluated as injectable tissue engineering materials in vivo. A suspension of murine fibroblasts in HA‐DTPH was crosslinked using PEGDA plus PEGDA peptide, and the viscous, gelling mixture was injected subcutaneously into the flanks of nude mice; gels formed in vivo following injection. After 4 weeks, growth of new fibrous tissue had been accelerated by the sense RGD peptides. Thus, attachment, spreading, and proliferation of cells is dramatically enhanced on RGD‐modified surfaces but only modestly accelerated in vivo tissue formation. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 68A: 365–375, 2004
Production of microspheres based on hydrophobically associating alginate derivatives by dispersion/gelation in aqueous sodium chloride solutions
Authors: Leonard M. , Rastello de Boisseson M. , Hubert P. , Dellacherie E. 
Published: December 2003

AbstractA new “all aqueous” procedure for the preparation of stable polysaccharide microparticles was developed. The method consists of dispersing a water solution of an amphiphilic alginate derivative (in the current work, alginate substituted with low amounts of dodecyl chains) first fluidified under mechanical stress, into an NaCl solution. The procedure exploits the ability of amphiphilic associative derivatives to form strong hydrogels in the presence of nonchaotropic salts and their shear‐thinning/thixotropic properties. Depending on the experimental conditions, the size of the microparticles can be varied from 10 μm to several hundred micrometers. Their mechanical properties can eventually be reinforced by addition of low concentrations of calcium chloride. The resulting microparticles exhibit a better stability than that of plain Ca2+‐alginate particles, as they are not disrupted when nongelling cations or calcium‐sequestering agents are added to the solution. In addition, the particles can be easily redispersed after being centrifuged or freeze‐dried. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 68A: 335–342, 2004
Growth behavior, matrix production, and gene expression of human osteoblasts in defined cylindrical titanium channels
Authors: Frosch Karl‐Heinz , Barvencik Florian , Viereck Volker , Lohmann Christoph H. , Dresing Klaus , Breme Jürgen , Brunner Edgar , Stürmer Klaus Michael 
Published: December 2003

AbstractThe purpose of the current study was to investigate the effect of different diameters of cylindrical titanium channels on human osteoblasts. Titanium samples having continuous drill channels with diameters of 300, 400, 500, 600, and 1000 μm were put into osteoblast cell cultures that were isolated from 12 adult human trauma patients. Cell migration into the drill channels was investigated by transmitted‐light microscopy. The DNA content in the drill channels was measured photometrically, collagen type I production was analyzed by enzyme‐linked immunosorbent assay (ELISA) and osteocalcin gene expression by reverse transcriptase–polymerase chain reaction (RT‐PCR). Formation of mineralized tissue was assessed by microradiographs of histological sections. Within 20 days, cells grew an average of 838 μm (±128 μm) into the drill channels with a diameter of 600 μm and were significantly faster (p < 0.05) than in all other channels. Cells produced significantly more osteocalcin messenger RNA (mRNA) in 600‐μm channels (p < 0.05) than they did in 1000‐μm channels and demonstrated the highest osteogenic differentiation. The channel diameter did not influence collagen type I production. The highest cell density was found in 300‐μm channels (p < 0.05). The DNA content of the channels linearly decreased with increasing channel diameters. After 40 days of culture, the proportion of mineralized tissue at the mouth section amounted to 6% in 300‐μm channels and to 9–11% in 400–600‐μm channels. In 1000‐μm channels, only traces of mineralization were detected. Our data suggest that the diameter of cylindrical titanium channels has a significant effect on migration, gene expression, and mineralization of human osteoblasts. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 68A: 325–334, 2004
Primary human marrow stromal cells and Saos‐2 osteosarcoma cells use different mechanisms to adhere to hydroxylapatite
Authors: Kilpadi Krista L. , Sawyer Amber A. , Prince Charles W. , Chang Pi‐Ling , Bellis Susan L. 
Published: December 2003

AbstractOne important step in bone formation on hard tissue implants is adhesion of osteoblast precursors to the implant surface. In this study, we used function‐blocking antibodies against integrin subunits to characterize the mechanisms used by human marrow stromal cells and Saos‐2 osteosarcoma cells to adhere to protein‐coated hydroxylapatite (HA). We found that Saos‐2 use both α5‐ and αv‐containing integrins, whereas stromal cells use αv‐containing integrins but not α5‐containing integrins, despite the presence of α5‐containing integrins on cell surfaces. On the basis of this difference, we examined binding of these cell types to HA coated with fibronectin (FN) or vitronectin (VN), to determine whether these ligands for α5 and αv integrins could enhance the numbers or morphology of cells adhered to them. We also examined the adhesion of cells to HA coated with RGD peptides designed to bind to FN or VN receptors. Morphology and number of adherent stromal cells were markedly enhanced on serum‐coated surfaces compared with FN or VN alone, whereas, surprisingly, Saos‐2 cells failed to spread on serum‐coated HA and displayed superior spreading and stress fiber formation on VN‐coated HA. Collectively, these results have important implications for the design of protein coatings to enhance the performance of HA implants. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 68A: 273–285, 2004
Fibroblast attachment to smooth and microtextured PET and thin cp‐Ti films
Authors: Jain Rakhi , von Recum Andreas F. 
Published: December 2003

AbstractImproving the biological performance of engineered implants apposing interfacing tissues is a critical issue in Biomaterials Science and Engineering. Micromotion at the soft tissue–implant interface has been shown to sustain an inflammatory response. To eliminate micromotion, it is desirable to promote cellular and extracellular matrix adhesion to the implant surface. Surfaces are modified topographically or chemically to effect cellular adhesion and to influence cellular interactions and function. Previous studies have identified the specific topographical characteristics that appear to elicit cellular attachment. This in vitro study compares the independent effects of surface chemistry and topography on fibroblast‐test specimen proximity. Titanium (Ti) was sputter‐coated in stepwise, increasing thickness (20–350 nm) onto a series of either smooth or microtextured polyethylene terephthalate (PET), resulting in a stepwise change from a PET surface to a Ti surface. The series was evaluated in a 3‐day fibroblast culture with transmission electron microscopy (TEM) for cell–test specimen proximity. Fibroblast proximity to the coverslip surface increases, as the Ti thickness increases, on either smooth or textured test specimens. Furthermore, fibroblasts were firmly attached to the ridge tops on the coated textured test specimens. Therefore, fibroblast apposition is strongly enhanced by microtextured surfaces and Ti rather than smooth surfaces and PET. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 68A: 296–304, 2004
Pitfalls in the detection of lipid vectors in neural cell culture and in brain tissue
Authors: Rizk T. , Montero‐Menei C. , Jollivet C. , Benoit J. P. , Menei P. 
Published: December 2003

AbstractLipid particles (liposomes and lipid‐coated microbubbles) are currently studied as vectors for drug delivery to the central nervous system. The visualization of these particles is usually based on their labeling with a lipophilic fluorescent dye (3,3′‐dioctadecycloxacarbocyanine perchlorate) or staining with Oil Red O. The purpose of this article was to highlight the difficulties and pitfalls encountered with the use of these techniques in the detection of lipid particles in neural cell cultures and in brain tissue. In vitro and in vivo studies were conducted on different neural cell cultures (rat and human tumors, microglial cells) and animal models of brain lesion (lipopolysaccharide and quinolinic acid‐induced lesion, induced brain tumor). The cells or brain slices were observed with optical microscopy after staining with Oil Red O, fluorescent microscopy, or scanning electron microscopy. Intra and extracytoplasmic lipid particles (stained with Oil Red O or autofluorescent or visualized by scanning electron microscopy) were naturally found in the cells and tissues studied. Intracytoplasmic lipid microparticles were present in tumoral and microglial cells. These lipid microparticles were also observed with some extracytoplasmic lipid droplets in the induced brain lesions. These images could be misinterpreted as lipid vectors if the cells or animals would have been treated with such a vector. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 68A: 360–364, 2004
Plasmapheresis for hyperlipidemic pancreatitis
Authors: Yeh Jiann‐Horng , Chen Jui‐Hao , Chiu Hou‐Chang 
Published: December 2003

AbstractPatients with triglyceride levels over 1,000 mg/dl are at high risk of developing acute pancreatitis. This study aimed to determine the effectiveness of plasma exchange (PE) in reducing triglyceride levels during an acute attack of hyperlipidemic pancreatitis (HLP). A total of 17 hypertriglyceridemic patients with the complication of acute pancreatitis received one course of PE treatment for one or two consecutive sessions. The respective mean removal rates during a single PE for triglyceride, cholesterol, amylase, and lipase were 66.3, 62.1, 70.0, and 84.8%, respectively. An additional one exchange increased the removal rate to 83.3, 66.2, 85.5, and 87.0%, respectively. For the two‐sessions of treatment, the removal rates were higher for triglyceride (P = 0.0015) and amylase with a borderline statistical significance (P = 0.0641). Better triglyceride clearance correlated well with lower levels of transmembrane pressure (TMP) at 90 minutes after PE (r2 = 0.5782, P = 0.0010) and shorter plasmapheresis duration (r2 = 0.2241, P = 0.0427). Thirteen of seventeen patients (76.5%) recovered completely, eight patients in a single‐session, and five in two‐sessions. Two patients developed intra‐abdominal abscess, necessitating surgical drainage and two patients died due to both septic shock and multi‐organ failure. No significant predictor of clinical outcome was identified. In summary, PE treatment is an effective method to clear lipids and enzymes from plasma in a single session for most HLP patients. A greater extraction of triglyceride would result in a reduced TMP and a shorter duration of PE treatment. J. Clin. Apheresis 18:181–185, 2003. © 2003 Wiley‐Liss, Inc.
Extracorporeal double filtration plasmapheresis in acute atherothrombotic brain infarction caused by major artery occlusive lesion
Authors: Hasegawa Yasuhiro , Tagaya Masafumi , Fujimoto Shigeru , Hayashida Kohei , Yamaguchi Takenori , Minematsu Kazuo 
Published: December 2003

AbstractExtracorporeal double filtration plasmapheresis (EDFP) can quickly lower plasma viscosity and fibrinogen concentration. EDFP has the potential to improve cerebral microcirculation in acute ischemic stroke and ultimately to salvage penumbral tissue. However, no evidence is available to show that EDFP can increase cerebra blood flow (CBF). Therefore, we investigated whether EDFP could increase CBF by quantitative CBF measurements and documented the clinical effects of EDFP in acute ischemic stroke. EDFP was performed ten times in seven patients diagnosed as having acute atherothrombotic brain infarction caused by major artery occlusive lesion. They also fulfilled one of the following entry criteria: 1) diffusion/perfusion mismatch demonstrated by MRI on admission; 2) a hemispheric syndrome, but only a small lesion on diffusion weighted MRI (<25% of MCA territory); or 3) progressing stroke. Exclusion criteria were 1) contraindication of heparin or 2) spontaneous improvement of symptoms. Time from stroke onset to EDFP varied from 5 hr to 7 days. Plasma viscosity was quickly lowered by EDFP without affecting RBC counts, Hb, or Hct in all patients. Positron emission tomography (PET) with 15‐O labeled H2O measurements revealed a significant CBF increase from 36.4±8.3 ml/100 g/min to 40.7±6.8 ml/100 g/min in the affected hemisphere (P=0.048). Definite CBF improvement was also demonstrated by single photon emission computed tomography (SPECT) in one of two patients who had severe stenosis of the middle cerebral artery. Furthermore, this patient showed remarkable improvement of hemiplegia immediately following EDFP (NIHSS score: 18 to 13). In conclusion, EDFP can increase CBF in ischemic brain tissue in acute atherothrombotic brain infarction. Further clinical studies should focus on the efficacy of EDFP on outcome of patients with this stroke subtype. J. Clin. Apheresis 18:167–174, 2003. © 2003 Wiley‐Liss, Inc.