bluuebunny/crossref_metadata_2025 huggingface dataset:
NAD(P)H Fluorescence Transients after Synaptic Activity in Brain Slices: Predominant Role of Mitochondrial Function
Authors: Brennan Angela M , Connor John A , Shuttleworth C William
Published: March 2006

Excitatory stimulation in hippocampal slices results in biphasic NAD(P)H fluorescence transients. Previous studies using differing stimulus protocols agreed that the oxidation phase is a consequence of mitochondrial metabolism, but the reduction phase has been attributed to (1) mitochondrial nicotinamide adenine dinucleotide (NADH) generation or (2) astrocytic glycolysis triggered by glutamate uptake. In an attempt to reconcile these two views, the present study examined NAD(P)H signals evoked by a wide range of stimulus durations (40 ms to 20secs). A combination of ionotropic glutamate receptor (iGluR) antagonists (6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), 2-amino-5-phosphonopentanoic acid (APV)) virtually abolished responses to brief stimuli (40 to 200 ms, 50 Hz), but a significant fraction of the signal elicited by extended stimulation (20 secs, 32 Hz) was resistant to CNQX/APV. Glycolysis was inhibited by removal of glucose and addition of 2-deoxyglucose (2DG) (10 mmol/l) or iodoacetic acid (IAA, 1 mmol/l). Pyruvate was provided as an alternative substrate for oxidative phosphorylation and the A1 receptor antagonist 1,3-Dipropyl-8-cyclopentylxanthine (DPCPX) included to prevent decreases in synaptic efficacy. If sufficient pyruvate was supplied, responses to brief and extended stimuli were unaffected by glycolytic inhibition and not significantly reduced by an inhibitor of glucose uptake (3- O-methyl glucose, 3 mmol/l). When timed to arrive at the peak of overshoots generated by extended synaptic stimulation, brief pyruvate applications (10 mmol/l, 2mins) had little effect on evoked NAD(P)H increases. Flavoprotein autofluorescence transients after extended stimuli matched (with inverted sign) NAD(P)H responses. Responses to extended stimuli were not reduced by a nonselective inhibitor of glutamate uptake DL-Threo-β-benzyloxyaspartic acid (TBOA). These results suggest that NAD(P)H transients report mitochondrial dynamics, rather than recruitment of glycolytic metabolism, over a wide range of stimulus intensities.
p53 Potentiates Hippocampal Neuronal Death Caused by Global Ischemia
Authors: Yonekura Ichiro , Takai Keisuke , Asai Akio , Kawahara Nobutaka , Kirino Takaaki
Published: March 2006

Although p53 controls cell death after various stresses, its role in neuronal death after brain ischemia is poorly understood. To address this issue, we subjected p53-deficient ( p53−/− and p53+/−) mice (backcrossed for 12 generations with C57BL/6 mice) and wild-type mice ( p53+/+) to transient global ischemia by the three-vessel occlusion method. Despite similar severity of ischemia, as shown by anoxic depolarization and cortical blood flow, neuronal death in the hippocampal cornus ammonis (CA)1 region was much more extensive in p53+/+ than in p53−/− mice (surviving neuronal count, 9.3% ± 3.0% versus 61.3% ± 34.0% of nonischemic p53+/+ controls, respectively, P < 0.0037). In p53+/− mice, a similar trend was also observed, though not statistically significant (43.5% of nonischemic p53+/+ controls). In p53+/+ mice, p53-like immunoreactivity in hippocampal CA1 neurons was enhanced at 12 h after ischemia, and messenger ribonucleic acid for Bax, a direct downstream target of p53, was also increased. These results indicate that p53 potentiates ischemic neuronal death in vivo and suggest that this molecule could be a therapeutic target in neuronal death after cerebral ischemia.
Time Course of Post-Traumatic Mitochondrial Oxidative Damage and Dysfunction in a Mouse Model of Focal Traumatic Brain Injury: Implications for Neuroprotective Therapy
Authors: Singh Indrapal N , Sullivan Patrick G , Deng Ying , Mbye Lamin H , Hall Edward D
Published: March 2006

In the present study, we investigate the hypothesis that mitochondrial oxidative damage and dysfunction precede the onset of neuronal loss after controlled cortical impact traumatic brain injury (TBI) in mice. Accordingly, we evaluated the time course of post-traumatic mitochondrial dysfunction in the injured cortex and hippocampus at 30 mins, 1, 3, 6, 12, 24, 48, and 72 h after severe TBI. A significant decrease in the coupling of the electron transport system with oxidative phosphorylation was observed as early as 30 mins after injury, followed by a recovery to baseline at 1 h after injury. A statistically significant ( P < 0.0001) decline in the respiratory control ratio was noted at 3 h, which persisted at all subsequent time-points up to 72 h after injury in both cortical and hippocampal mitochondria. Structural damage seen in purified cortical mitochondria included severely swollen mitochondria, a disruption of the cristae and rupture of outer membranes, indicative of mitochondrial permeability transition. Consistent with this finding, cortical mitochondrial calcium-buffering capacity was severely compromised by 3h after injury, and accompanied by significant increases in mitochondrial protein oxidation and lipid peroxidation. A possible causative role for reactive nitrogen species was suggested by the rapid increase in cortical mitochondrial 3-nitrotyrosine levels shown as early as 30 mins after injury. These findings indicate that post-traumatic oxidative lipid and protein damage, mediated in part by peroxynitrite, occurs in mitochondria with concomitant ultrastructural damage and impairment of mitochondrial bioenergetics. The data also indicate that compounds which specifically scavenge peroxynitrite (ONOO) or ONOO−derived radicals (e.g. ONOO− + H+ → ONOOH → †NO2 + †OH) may be particularly effective for the treatment of TBI, although the therapeutic window for this neuroprotective approach might only be 3 h.
Differential Recovery of Multimodal MRI and Behavior after Transient Focal Cerebral Ischemia in Rats
Authors: Sicard Kenneth M , Henninger Nils , Fisher Marc , Duong Timothy Q , Ferris Craig F
Published: March 2006

The association between recovery of brain function and behavior after transient cerebral ischemia in animals and humans is incompletely characterized. Quantitative diffusion- (DWI), perfusion- (PWI), T2-weighted (T2WI), and functional magnetic resonance imaging (fMRI) were performed before, during, and up to 1 day after 20-mins transient middle cerebral artery occlusion (tMCAO; n = 6) or sham operation (n = 6) in male Sprague-Dawley rats. Viability thresholds were employed to calculate diffusion, perfusion, and T2 lesion volumes. Region of interest analysis was used to evaluate structural and functional MR signal changes within the sensorimotor network, which were then related to corresponding behavioral measures. Post-mortem 2,3,5-triphenyltetrazolium chloride (TTC) staining was performed 24 h after ischemia. Transient middle cerebral artery occlusion produced lesions on DWI and PWI, which fully recovered by 30 mins after reperfusion. Ipsilesional fMRI responses to hypercapnia and forepaw stimulation were significantly impaired after ischemia and did not fully normalize until 3 and 24 h after tMCAO, respectively. No abnormalities were observed on imaging or TTC at 24 h despite significant behavioral dysfunctions including contralesional forelimb impairment and ipsilesional neglect. No MRI, behavioral, or TTC anomalies were observed in sham-operated rats. There were no significant correlations between MRI parameters, behavior, and TTC in either group. Together, these results suggest that normal findings on diffusion, perfusion, and T2 imaging shortly after transient ischemia may not indicate normal tissue status as indicated by fMRI and behavior, which may help explain the persistence of neurologic deficits in patients with normal conventional MRI after cerebral ischemia.
Activation of the Akt/GSK3β Signaling Pathway Mediates Survival of Vulnerable Hippocampal Neurons after Transient Global Cerebral Ischemia in Rats
Authors: Endo Hidenori , Nito Chikako , Kamada Hiroshi , Nishi Tatsuro , Chan Pak H
Published: March 2006

Recent studies have revealed that the phosphatidylinositol 3-kinase (PI3-K) pathway is involved in apoptotic cell death after experimental cerebral ischemia. The serine—threonine kinase, Akt, functions in the PI3-K pathway and prevents apoptosis by phosphorylation at Ser473 after a variety of cell death stimuli. After phosphorylation, activated Akt inactivates other apoptogenic factors, including glycogen synthase kinase-3β (GSK3β), thereby inhibiting cell death. However, the role of Akt/GSK3β signaling in the delayed death of hippocampal neurons in the CA1 subregion after transient global cerebral ischemia (tGCI) has not been clarified. Transient global cerebral ischemia for 5 mins was induced by bilateral common carotid artery occlusion combined with hypotension. Western blot analysis showed a significant increase in phospho-Akt (Ser473) and phospho-GSK3β (Ser9) in the hippocampal CA1 subregion after tGCI. Immunohistochemistry showed that expression of phospho-Akt (Ser473) and phospho-GSK3β (Ser9) was markedly increased in the vulnerable CA1 subregion, but not in the ischemic-tolerant CA3 subregion. Double staining with phospho-GSK3β (Ser9) and terminal deoxynucleotidyl transferase-mediated uridine 5ʼ-triphosphate-biotin nick end labeling showed different cellular distributions in the CA1 subregion 3 days after tGCI. Phosphorylation of Akt and GSK3β was prevented by LY294002, a PI3-K inhibitor, which facilitated subsequent DNA fragmentation 3 days after tGCI. Moreover, transgenic rats that overexpress copper/zinc-superoxide dismutase, which is known to be neuroprotective against delayed hippocampal CA1 injury after tGCI, had enhanced and persistent phosphorylation of both Akt and GSK3β after tGCI. These findings suggest that activation of the Akt/GSK3β signaling pathway may mediate survival of vulnerable hippocampal CA1 neurons after tGCI.
Functional complementation of truncated human skeletal-muscle chloride channel (hClC-1) using carboxyl tail fragments
Authors: Wu Weiping , Rychkov Grigori Y. , Hughes Bernard P. , Bretag Allan H.
Published: March 2006

Crystal structures of bacterial CLC (voltage-gated chloride channel family) proteins suggest the arrangement of permeation pores and possible gates in the transmembrane region of eukaryotic CLC channels. For the extensive cytoplasmic tails of eukaryotic CLC family members, however, there are no equivalent structural predictions. Truncations of cytoplasmic tails in different places or point mutations result in loss of function or altered gating of several members of the CLC family, suggesting functional importance. In the present study, we show that deletion of the terminal 100 amino acids (N889X) in human ClC-1 (skeletal-muscle chloride channel) has minor consequences, whereas truncation by 110 or more amino acids (from Q879X) destroys channel function. Use of the split channel strategy, co-injecting mRNAs and expressing various complementary constructs in Xenopus oocytes, confirms the importance of the Gln879–Arg888 sequence. A split between the two CBS (cystathionine β-synthase) domains (CBS1 and CBS2) gives normal function (e.g. G721X plus its complement), whereas a partial complementation, eliminating the CBS1 domain, eliminates function. Surprisingly, function is retained even when the region Gly721–Ala862 (between CBS1 and CBS2, and including most of the CBS2 domain) is omitted from the complementation. Furthermore, even shorter peptides from the CBS2-immediate post-CBS2 region are sufficient for functional complementation. We have found that just 26 amino acids from Leu863 to Arg888 are necessary since channel function is restored by co-expressing this peptide with the otherwise inactive truncation, G721X.
Structure–activity relationships of the human prothrombin kringle-2 peptide derivative NSA9: anti-proliferative activity and cellular internalization
Authors: Hwang Hyun Sook , Kim Dong Won , Kim Soung Soo
Published: March 2006

The human prothrombin kringle-2 protein inhibits angiogenesis and LLC (Lewis lung carcinoma) growth and metastasis in mice. Additionally, the NSA9 peptide (NSAVQLVEN) derived from human prothrombin kringle-2 has been reported to inhibit the proliferation of BCE (bovine capillary endothelial) cells and CAM (chorioallantoic membrane) angiogenesis. In the present study, we examined the structure–activity relationships of the NSA9 peptide in inhibiting the proliferation of endothelial cells lines e.g. BCE and HUVE (human umbilical vein endothelial). N- or C-terminal truncated derivatives and reverse sequence analogues of NSA9 were prepared and their anti-proliferative activities were assessed using the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide] assay. This cell proliferation assay demonstrated that both the N-terminal region and sequence orientation of NSA9 are important for inhibiting the proliferation of endothelial cells. In particular 2 C-terminal truncation derivatives of NSA9 [NSA7 (NSAVQLV) and NSA8 (NSAVQLVE)] inhibited cellular proliferation to a greater extent than did NSA9. The heptapeptide NSA7, was found to be more potent than NSA9 in inhibiting CAM angiogenesis, and tubular formation and migration of HUVE cells. In addition NSA9, NSA8 and NSA7 peptides exhibited considerable inhibitory effects on the proliferation of tumour cells such as B16F10 (murine melanoma), LLC and L929 (murine fibroblast). Also, cellular internalization studies demonstrated that NSA7 was internalized into both endothelial and tumour cells more easily than was NSA9. In conclusion, these results suggest that NSA7, residing within the full sequence of NSA9, contains the required sequence for anti-proliferative activity and cellular internalization.
Kinetic analysis using low-molecular mass xyloglucan oligosaccharides defines the catalytic mechanism of a Populus xyloglucan endotransglycosylase
Authors: Saura-Valls Marc , Fauré Régis , Ragàs Sergi , Piens Kathleen , Brumer Harry , Teeri Tuula T. , Cottaz Sylvain , Driguez Hugues , Planas Antoni
Published: March 2006

Plant XETs [XG (xyloglucan) endotransglycosylases] catalyse the transglycosylation from a XG donor to a XG or low-molecular-mass XG fragment as the acceptor, and are thought to be important enzymes in the formation and remodelling of the cellulose-XG three-dimensional network in the primary plant cell wall. Current methods to assay XET activity use the XG polysaccharide as the donor substrate, and present limitations for kinetic and mechanistic studies of XET action due to the polymeric and polydisperse nature of the substrate. A novel activity assay based on HPCE (high performance capillary electrophoresis), in conjunction with a defined low-molecular-mass XGO {XG oligosaccharide; (XXXGXXXG, where G=Glcβ1,4- and X=[Xylα1,6]Glcβ1,4-)} as the glycosyl donor and a heptasaccharide derivatized with ANTS [8-aminonaphthalene-1,3,6-trisulphonic acid; (XXXG-ANTS)] as the acceptor substrate was developed and validated. The recombinant enzyme PttXET16A from Populus tremula x tremuloides (hybrid aspen) was characterized using the donor/acceptor pair indicated above, for which preparative scale syntheses have been optimized. The low-molecular-mass donor underwent a single transglycosylation reaction to the acceptor substrate under initial-rate conditions, with a pH optimum at 5.0 and maximal activity between 30 and 40 °C. Kinetic data are best explained by a ping-pong bi-bi mechanism with substrate inhibition by both donor and acceptor. This is the first assay for XETs using a donor substrate other than polymeric XG, enabling quantitative kinetic analysis of different XGO donors for specificity, and subsite mapping studies of XET enzymes.
Weaning-induced expression of a milk-fat globule protein, MFG-E8, in mouse mammary glands, as demonstrated by the analyses of its mRNA, protein and phosphatidylserine-binding activity
Authors: Nakatani Hajime , Aoki Naohito , Nakagawa Yoshimi , Jin-No Shinji , Aoyama Koji , Oshima Kenji , Ohira Sachiyo , Sato Chihiro , Nadano Daita , Matsuda Tsukasa
Published: March 2006

A milk membrane glycoprotein, MFG-E8 [milk fat globule-EGF (epidermal growth factor) factor 8], is expressed abundantly in lactating mammary glands in stage- and tissue-specific manners, and has been believed to be secreted in association with milk fat globules. In the present paper, we describe further up-regulation of MFG-E8 in involuting mammary glands, where the glands undergo a substantial increase in the rate of epithelial cell apoptosis, and a possible role of MFG-E8 in mediating recognition and engulfment of apoptotic cells through its specific binding to PS (phosphatidylserine). Immunoblotting and RNA blotting analyses revealed that both MFG-E8 protein and MFG-E8 mRNA were markedly increased in mammary tissue within 3 days of either natural or forced weaning (pup withdrawal) of lactating mice. Using immunohistochemical analysis of the mammary tissue cryosections, the MFG-E8 signal was detected around the epithelium of such involuting mammary glands, but was almost undetectable at early- and mid-lactation stages, although strong signals were obtained for milk fat globules stored in the alveolar lumen. Some signals double positive to a macrophage differentiation marker, CD68, and MFG-E8 were detected in the post-weaning mammary tissue, although such double-positive signals were much smaller in number than the MFG-E8 single-positive ones. Total MFG-E8 in milk was also increased in the post-weaning mammary glands and, furthermore, the free MFG-E8 content in the post-weaning milk, as measured by in vitro PS-binding and apoptotic HC11 cell-binding activities, was much higher than that of lactation. In addition, the post-weaning milk enhanced the binding of apoptotic HC11 cells to J774 macrophages. Sucrose density-gradient ultracentrifugation analyses revealed that such enhanced PS-binding activity of MFG-E8 was present in membrane vesicle fractions (density 1.05–1.13 g/ml), rather than milk fat globule fractions. The weaning-induced MFG-E8 might play an important role in the recognition and engulfment of apoptotic epithelial cells by the neighbouring phagocytic epithelial cells in involuting mammary glands.
Mechanistic characterization of the MSDH (methylmalonate semialdehyde dehydrogenase) from Bacillus subtilis
Authors: Stines-Chaumeil Claire , Talfournier François , Branlant Guy
Published: March 2006

Homotetrameric MSDH (methylmalonate semialdehyde dehydrogenase) from Bacillus subtilis catalyses the NAD-dependent oxidation of MMSA (methylmalonate semialdehyde) and MSA (malonate semialdehyde) into PPCoA (propionyl-CoA) and acetyl-CoA respectively via a two-step mechanism. In the present study, a detailed mechanistic characterization of the MSDH-catalysed reaction has been carried out. The results suggest that NAD binding elicits a structural imprinting of the apoenzyme, which explains the marked lag-phase observed in the activity assay. The enzyme also exhibits a half-of-the-sites reactivity, with two subunits being active per tetramer. This result correlates well with the presence of two populations of catalytic Cys302 in both the apo- and holo-enzymes. Binding of NAD causes a decrease in reactivity of the two Cys302 residues belonging to the two active subunits and a pKapp shift from approx. 8.8 to 8.0. A study of the rate of acylation as a function of pH revealed a decrease in the pKapp of the two active Cys302 residues to approx. 5.5. Taken to-gether, these results support a sequential Cys302 activation process with a pKapp shift from approx. 8.8 in the apo-form to 8.0 in the binary complex and finally to approx. 5.5 in the ternary complex. The rate-limiting step is associated with the β-decarboxylation process which occurs on the thioacylenzyme intermediate after NADH release and before transthioesterification. These data also indicate that bicarbonate, the formation of which is enzyme-catalysed, is the end-product of the reaction.
Molecular and functional characterization of a novel gonadotropin-releasing-hormone receptor isolated from the common octopus (Octopus vulgaris)
Authors: Kanda Atsuhiro , Takahashi Toshio , Satake Honoo , Minakata Hiroyuki
Published: March 2006

GnRH (gonadotropin-releasing hormone) plays a pivotal role in the regulation of reproduction in vertebrates through interaction with a specific receptor. Previously, we isolated a GnRH homo-logue, oct-GnRH, from the common octopus (Octopus vulgaris). In the present study, we have identified a GnRH receptor (oct-GnRHR) specific for oct-GnRH from Octopus brain. Oct-GnRHR includes domains and motifs typical of vertebrate GnRH receptors. The intron-inserted positions are conserved between oct-GnRHR and the chordate GnRHR genes. The oct-GnRHR expressed in Xenopus (South African clawed frog) oocytes was responsive to oct-GnRH, but not to any other HPLC fractions of the Octopus brain extract. These results show that oct-GnRHR is an authentic receptor for oct-GnRH. Southern blotting of reverse-transcription PCR products revealed that the oct-GnRHR mRNA was widely distributed in the central and peripheral nervous systems and in several peripheral tissues. In situ hybridiz-ation showed that oct-GnRHR mRNA was expressed in some regions involved in autonomic functions, feeding, memory and movement. Oct-GnRH was shown to induce steroidogenesis of testosterone, progesterone and 17β-oestradiol in Octopus ovary and testis, where oct-GnRHR was abundantly expressed. These results suggest that oct-GnRH, like its vertebrate counterparts, acts as a multifunctional neurotransmitter, neuromodulator and hormone-like factor, both in Octopus central nervous system and peripheral tissues, and that both structure and functions of the GnRH family are, at least partially, evolutionarily conserved between octopuses and chordates.
Intracellular localization of p40, a protein identified in a preparation of lysosomal membranes
Authors: Boonen Marielle , Hamer Isabelle , Boussac Muriel , Delsaute Anne-Françoise , Flamion Bruno , Garin Jérôme , Jadot Michel
Published: March 2006

Unlike lysosomal soluble proteins, few lysosomal membrane proteins have been identified. Rat liver lysosomes were purified by centrifugation on a Nycodenz density gradient. The most hydrophobic proteins were extracted from the lysosome membrane preparation and were identified by MS. We focused our attention on a protein of approx. 40 kDa, p40, which contains seven to ten putative transmembrane domains and four lysosomal consensus sorting motifs in its sequence. Knowing that preparations of lysosomes obtained by centrifugation always contain contaminant membranes, we combined biochemical and morphological methods to analyse the subcellular localization of p40. The results of subcellular fractionation of mouse liver homogenates validate the lysosomal residence of p40. In particular, a density shift of lysosomes induced by Triton WR-1339 similarly affected the distributions of p40 and β-galactosidase, a lysosomal marker protein. We confirmed by fluorescence microscopy on eukaryotic cells transfected with p40 or p40–GFP (green fluorescent protein) constructs that p40 is localized in lysosomes. A first molecular characterization of p40 in transfected Cos-7 cells revealed that it is an unglycosylated protein tightly associated with membranes. Taken together, our results strongly support the hypothesis that p40 is an authentic lysosomal membrane protein.
A novel subfamily of monomeric inorganic pyrophosphatases in photosynthetic eukaryotes
Authors: Gómez-García María R. , Losada Manuel , Serrano Aurelio
Published: March 2006

Two sPPases (soluble inorganic pyrophosphatases, EC 3.6.1.1) have been isolated from the microalga Chlamydomonas reinhardtii. Both are monomeric proteins of organellar localization, the chloroplastic sPPase I [Cr (Ch. reinhardtii)-sPPase I, 30 kDa] is a major isoform and slightly larger protein than the mitochondrial sPPase II (Cr-sPPase II, 24 kDa). They are members of sPPase family I and are encoded by two different cDNAs, as demonstrated by peptide mass fingerprint analysis. Molecular phylogenetic analyses indicated that Cr-sPPase I is closely related to other eukaryotic sPPases, whereas Cr-sPPase II resembles its prokaryotic counterparts. Chloroplastic sPPase I may have replaced a cyanobacterial ancestor very early during plastid evolution. Cr-sPPase II orthologues are found in members of the green photosynthetic lineage, but not in animals or fungi. These two sPPases from photosynthetic eukaryotes are novel monomeric family I sPPases with different molecular phylogenies and cellular localizations.
Enhanced levels of Pis1p (phosphatidylinositol synthase) improve the growth of Saccharomyces cerevisiae cells deficient in Rsp5 ubiquitin ligase
Authors: Kaliszewski Pawel , Ferreira Thierry , Gajewska Beata , Szkopinska Anna , Berges Thierry , Żołądek Teresa
Published: March 2006

The Rsp5 ubiquitin ligase plays a role in many cellular processes including the biosynthesis of unsaturated fatty acids. The PIS1 (phosphatidylinositol synthase gene) encoding the enzyme Pis1p which catalyses the synthesis of phosphatidylinositol from CDP-diacyglycerol and inositol, was isolated in a screen for multicopy suppressors of the rsp5 temperature sensitivity phenotype. Suppression was allele non-specific. Interestingly, expression of PIS1 was 2-fold higher in the rsp5 mutant than in wild-type yeast, whereas the introduction of PIS1 in a multicopy plasmid increased the level of Pis1p 6-fold in both backgrounds. We demonstrate concomitantly that the expression of INO1 (inositol phosphate synthase gene) was also elevated approx. 2-fold in the rsp5 mutant as compared with the wild-type, and that inositol added to the medium improved growth of rsp5 mutants at a restrictive temperature. These results suggest that enhanced phosphatidylinositol synthesis may account for PIS1 suppression of rsp5 defects. Analysis of lipid extracts revealed the accumulation of saturated fatty acids in the rsp5 mutant, as a consequence of the prevention of unsaturated fatty acid synthesis. Overexpression of PIS1 did not correct the cellular fatty acid content; however, saturated fatty acids (C16:0) accumulated preferentially in phosphatidylinositol, and (wild-type)-like fatty acid composition in phosphatidylethanolamine was restored.
Clustering of heat-shock factors
Authors: Björk Johanna K. , Sistonen Lea
Published: March 2006

Clusterin is a ubiquitous glycoprotein found in most physiological fluids and tissues. Although not fully understood, the function of clusterin seems to be related to its ability to bind a wide variety of molecules. Since clusterin has been found associated with extracellular protein aggregates, a role as a molecular chaperone has been proposed. In this issue of the Biochemical Journal, Le Dréan and colleagues demonstrate an up-regulation of clusterin in neuronal cells exposed to proteotoxic stress that results in unfolded protein accumulation and proteasome impairment, both commonly associated with neurodegenerative diseases. Interestingly, expression of clusterin was found to be regulated by two members of the HSF (heat-shock factor) family, HSF1 and HSF2, which possibly form a trimeric complex on the clusterin promoter. The study proposes clusterin as a player in a cellular defence mechanism against harmful protein accumulation, and highlights the importance of elucidating further the exact role of clusterin and the intriguing interaction between HSF1 and HSF2.
Insulin-like growth factor-binding protein-5 (IGFBP-5): a critical member of the IGF axis
Authors: Beattie James , Allan Gordon J. , Lochrie Jennifer D. , Flint David J.
Published: March 2006

The six members of the insulin-like growth factor-binding protein family (IGFBP-1–6) are important components of the IGF (insulin-like growth factor) axis. In this capacity, they serve to regulate the activity of both IGF-I and -II polypeptide growth factors. The IGFBPs are able to enhance or inhibit the activity of IGFs in a cell- and tissue-specific manner. One of these proteins, IGFBP-5, also has an important role in controlling cell survival, differentiation and apoptosis. In this review, we report on the structural and functional features of the protein which are important for these effects. We also examine the regulation of IGFBP-5 expression and comment on its potential role in tumour biology, with special reference to work with breast cancer cells.
Haemoglobin and flow-mediated vasodilation
Authors: Madsen Per Lav , Scheuermann Freestone Michaela , Neubauer Stefan , Channon Keith , Clarke Kieran
Published: March 2006

A low [Hb] (Hb concentration) is out-balanced by peripheral vasodilation via mechanisms that are incompletely understood. Peripheral vasodilation is influenced by NO (nitric oxide) released from vascular endothelium in response to increased vessel wall shear stress, and absorption by Hb is the main mechanism by which the bioactivity of NO is disarmed. Thus we propose that graded NO absorption is the mechanism through which a low [Hb] is related to peripheral vasodilation. In the present study, we examined the relationship between [Hb] and FMD (flow-mediated vasodilation; 5 min of cuff ischaemia) of the radial and brachial arteries in 33 normal subjects and in 13 patients with Type II diabetes, known to have impaired NO-mediated vasodilation. The smaller radial artery provided the more sensitive test, as it had a 2-fold larger FMD than the brachial artery (22±18% compared with 9±18% respectively, in normal subjects; means±S.D., P<0.05). FMD of the radial artery had a negative correlation with [Hb] (r2=−0.66, P<0.05; n=27). In subjects with [Hb] below and above the median of 14.1 g/dl, the radial artery FMD was 30±22% compared with 13±12% respectively (P<0.05). In diabetic patients, FMD was lower and a co-variation with [Hb] could not be established. Thus, in normal subjects, NO-mediated endothelium-related vasodilation at least partly out-balanced the ‘added burden’ of a low [Hb] during post-ischaemic reperfusion.
Trapping, dark current, and wave breaking in nonlinear plasma waves
Authors: Schroeder C. B. , Esarey E. , Shadwick B. A. , Leemans W. P.
Published: March 2006

The trapping of thermal electrons in a nonlinear electron plasma wave of arbitrary phase velocity is investigated. Using a model based on single-particle dynamics, various thermal effects are calculated, such as the evolution of the plasma temperature. Assuming a broad (one-dimensional) plasma wave driver, the threshold plasma wave amplitude for electron trapping is calculated, thereby determining the fraction of trapped plasma electrons and the expected dark current in a plasma-based accelerator. It is shown that the trapping threshold is increased within the region of the laser pulse. The laser intensity required to excite plasma waves of sufficient amplitude to trap background electrons is determined. The hydrodynamic wave breaking field amplitude is recovered from particle trapping considerations. Implications for experimental and numerical studies of plasma accelerators are discussed.
Plasma-sheath effects on the Debye screening problem
Authors: Sarmah D. , Tessarotto M. , Salimullah M.
Published: March 2006

The classical Debye-Hückel screening effect of the electrostatic field generated by isolated charged particles immersed in a plasma is reviewed. The validity of the underlying mathematical model, and particularly of the weak-field approximation, is analyzed. It is shown that the presence of the plasma sheath around test particles and the resulting effect of charge screening are essential for the description of plasmas that are strongly coupled.
Mechanical crosstalk between vertical and lateral piezoresponse force microscopy
Authors: Peter F. , Rüdiger A. , Waser R.
Published: March 2006

Piezoresponse force microscopy (PFM) provides valuable insight into the inverse lateral and vertical piezoelectric effects on the nanoscale. Ideally, these contributions are separated into vertical and lateral detections of a deflected laser beam on a quadrupole diode. In contrast to the known crosstalk by a rotated diode that causes identical signals in both channels, we report on the crosstalk due to the geometrical constraints of the cantilever that is inherent to the lateral PFM. For a BaTiO3 (001) nanograin we show that the vertical response attributable to the crosstalk is 1∕8th of the lateral response. From this value we deduce the actual mechanism responsible for the crosstalk.
On the ϵ-ζ transition of nitrogen
Authors: Gregoryanz Eugene , Sanloup Chrystèle , Bini Roberto , Kreutz Jörg , Jodl Hans J. , Somayazulu Maddury , Mao Ho-kwang , Hemley Russell J.
Published: March 2006

Group theory analysis and synchrotron x-ray diffraction measurements show that the recently proposed crystal structure of ζ-nitrogen is inconsistent with the available experimental data for that phase.
Neoclassical generation of toroidal zonal flow by drift wave turbulence
Authors: Mikhailovskii A. B. , Smolyakov A. I. , Tsypin V. S. , Kovalishen E. A. , Shirokov M. S. , Galvão R. M. O.
Published: March 2006

Zonal-flow instabilities due to drift-wave turbulence in the presence of toroidicity-induced parallel (neoclassical) viscosity and allowing for the toroidal flow are studied. It is shown that, as a result of the neoclassical viscosity a new type of zonal-flow instability is possible, leading to the generation of the considerable toroidal zonal flow. The toroidal instability is complementary to the previously studied instability resulting in the poloidal flow generation and occurs as a second branch of the general dispersion relation describing the evolution of the poloidal and toroidal flow. Nonlinear saturation of the new instability is studied. It is shown that saturated zonal toroidal velocity, generated in this instability, is large compared to the mean cross-field drift velocity as the ratio q∕ϵ, where q is the safety factor and ϵ is the inverse aspect ratio. In addition to the broad turbulent spectrum of drift waves, a monochromatic wave packet is considered. It is revealed that for the case of sufficiently strong neoclassical viscosity such a wave packet is subjected to generation of the toroidal zonal flow due to instability of hydrodynamic type.
The quantum fidelity for the time-periodic singular harmonic oscillator
Authors: Combescure Monique
Published: March 2006

In this paper we perform an exact study of “quantum fidelity” (also called Loschmidt echo) for the time-periodic quantum harmonic oscillator of the following Hamiltonian: Ĥg(t)≔(P2∕2)+f(t)(Q2∕2)+(g2∕Q2), when compared with the quantum evolution induced by Ĥ0(t) (g=0), in the case where f is a T-periodic function and g a real constant. The reference (initial) state is taken to be an arbitrary “generalized coherent state” in the sense of Perelomov. We show that, starting with a quadratic decrease in time in the neighborhood of t=0, this quantum fidelity may recur to its initial value 1 at an infinite sequence of times tk. We discuss the result when the classical motion induced by Hamiltonian Ĥ0(t) is assumed to be stable versus unstable.
Drift-magnetohydrodynamical model of error-field penetration in tokamak plasmas
Authors: Cole A. , Fitzpatrick R.
Published: March 2006

A previously published magnetohydrodynamical (MHD) model of error-field penetration in tokamak plasmas is extended to take drift-MHD physics into account. In particular, diamagnetic and semicollisional effects are both fully incorporated into the analysis. The new model is used to examine the scaling of the penetration threshold in ohmic tokamak plasmas.
Influence of the boundary conditions on the H-mode power threshold
Authors: Kalupin D. , Tokar M. Z. , Unterberg B. , Loozen X. , Pilipenko D. , Zagorski R. ,   TEXTOR Contributors
Published: March 2006

The effect of boundary conditions at the last closed magnetic surface (LCMS) on the formation of the edge transport barrier (ETB) in tokamaks is investigated by one-dimensional transport calculations for the radial profiles of plasma parameters. For a given heating power the transition from the low confinement mode (L mode) to the high confinement mode (H mode) can be triggered by increasing the density e-folding length, δn, or reducing the temperature e-folding length, δT, at the LCMS. This is explained by the decrease of heat losses from the confined plasma with the convection of charged particles and changeover to the case where losses are mostly due to heat conduction. In such a case, corresponding to a divertor configuration, the computed power threshold for the L- to H-mode transition (L-H transition) is in a good agreement with the experimental multimachine scaling.
Critical comparison of classical and quantum mechanical treatments of the phase equilibria of water
Authors: Wick Collin D. , Schenter Gregory K.
Published: March 2006

The Gibbs ensemble Monte Carlo simulation technique was used to compare the phase equilibria of the rigid TIP4P water model [Jorgensen et al., J. Chem. Phys. 79, 926 (1983)] utilizing classical and quantum statistical mechanics. The quantum statistical mechanical treatment generally resulted in lower liquid densities and higher vapor densities, narrowing the phase envelope. As a result, the calculated critical temperatures and normal boiling points were lower from the quantum simulations than the classical by 22 and 17K, respectively, but the critical densities were equal within the estimated uncertainties. When the phase diagram from the quantum statistical mechanical treatment was increased by 22K, it agreed with the classical results quite well throughout the entire simulated temperature range. A semiclassical treatment, involving a low order expansion in Planck’s constant, resulted in good agreement with the path integral results for second virial coefficients, but gave densities and vapor pressures that fluctuated between the values for the classical and quantum statistical mechanics values, with no definite agreement with either.
Influence of a finite initial ion density gradient on plasma expansion into a vacuum
Authors: Grismayer T. , Mora P.
Published: March 2006

The influence of a finite initial ion density gradient on a plasma expansion into a vacuum is studied with a numerical model that takes into account the charge-separation effects and assumes a Boltzmann equilibrium for the electrons. The cases of a semi-infinite plasma and of a finite plasma slab are treated. In both cases it is shown that the finite initial ion density gradient of the plasma surface leads to two phases in the plasma expansion, separated by a wave breaking of the ion flow. An ion front forms after the wave breaking and, in the semi-infinite plasma case, the plasma expansion becomes closer and closer to the initially sharp boundary case, the maximum ion velocity increasing logarithmically with time. In the finite plasma slab case, the energy conservation has to be taken into account, the thermal electron energy being progressively converted into the kinetic energy of the ions. When the initial ion density scale length lss is larger than a few percent of the total plasma slab width, the final maximum ion velocity decreases with lss.
Vibronic spectroscopy of the peroxyacetyl radical in the near IR
Authors: Hu Y. J. , Fu H. B. , Bernstein E. R.
Published: March 2006

The ÃA′2←X̃A″2 electronic transition of the peroxyacetyl radical (PA) is observed employing NIR/VUV ion enhancement, supersonic jet spectroscopy. Rotational envelope simulations yield a rotational temperature for ground state PA of ca. 55K. Ab initio calculations of transition energies and vibrational frequencies for the Ã←X̃ transition assist in the assignment of the observed spectrum. A number of the vibrational modes of the Ã state are assigned to observed transitions (the O–O stretch 21, the COO bend 51, and the CCOO backbone bend 61). The calculations and mass spectra suggest that the ground state of the PA ion is repulsive. An increase in rotational linewidth of the overtone of the O–O stretch (21) is observed and discussed in terms of Ã state dynamics. The O–O stretch anharmonicity is estimated to be 13.35cm−1.
Electrical characterization of amorphous lanthanum aluminate thin films grown by molecular-beam deposition on silicon
Authors: Edge L. F. , Schlom D. G. , Sivasubramani P. , Wallace R. M. , Holländer B. , Schubert J.
Published: March 2006

Amorphous LaAlO3 thin films were deposited at room temperature directly on n-type and p-type Si (001) by molecular beam deposition. The dielectric properties of the stoichiometric amorphous LaAlO3 thin films deposited on silicon were determined through capacitance-voltage and current-voltage measurements. The electrical measurements indicate that the amorphous LaAlO3 thin films have a dielectric constant (K) of K=16±2. This is significantly lower than the K=24 of crystalline LaAlO3. The equivalent oxide thickness values range between 9.8 and 15.5Å for films deposited on n-type silicon with physical thicknesses of 45–75Å.
Magnetic iron silicide nanowires on Si(110)
Authors: Liang S. , Islam R. , Smith David J. , Bennett P. A. , O’Brien J. R. , Taylor B.
Published: March 2006

Self-assembled iron silicide nanowires were formed by depositing 1ML of Fe onto Si(110) at 700°C in ultrahigh vacuum. The nanowires have average dimensions of 5nm high ×10nm wide ×μm long, as measured with ex situ atomic force microscopy. High-resolution electron microscopy identifies the crystal structure as cubic FeSi2 with orientation FeSi2(1¯11)∕∕Si(11¯1), FeSi2⟨110⟩∕∕Si⟨110⟩. Magnetometer measurements show a magnetic moment of 0.3Bohr magneton per iron atom at 2K. This magnetic property in metastable cubic FeSi2 nanowires opens up the possibility for high-density data storage and logic applications.
Anomalous electrical performance of nanoscaled interfacial oxides for bonded n-GaAs wafers
Authors: Ouyang Hao , Wu YewChung Sermon , Chiou Hsiao-Hao , Liu Chia-Cheng , Cheng Ji-Hao , Ouyang Wen , Chiou Shan-Haw , Shiue Sham-Tsong , Chueh Y. L. , Chou L. J.
Published: March 2006

Electrical performance was found to be closely related to the variation of nanosized interface morphology in previous studies. This work investigated in detail the microstructural development of in- and anti-phase bonded interfaces for n-type (100) GaAs wafers treated at 500, 600, 700 and 850°C. The interfacial energy of anti-phase bonding is higher than that of in-phase bonding based on the first-principles calculations. The higher interface energy tends to stabilize the interfacial oxide layer. The continuous interfacial oxide layer observed below 700°C can deteriorate the electrical property due to its insulating property. However, the existence of nanoscaled oxide at anti-phase bonded interfaces can improve the electrical conductivity at 700°C. This is due to the suppression of the evaporation of As atom by the interfacial nanoscaled oxides based on the analysis of autocorrelation function and energy dispersive x-ray spectroscopy.
Metal gate work function engineering using AlNx interfacial layers
Authors: Alshareef H. N. , Luan H. F. , Choi K. , Harris H. R. , Wen H. C. , Quevedo-Lopez M. A. , Majhi P. , Lee B. H.
Published: March 2006

Metal gate work function enhancement using thin AlNx interfacial layers has been evaluated. It was found that band edge effective work functions (∼5.10eV) can be achieved on hafnium-based high dielectric constant (high-k) materials using the AlNx interfacial layer and TiSiN electrodes. It was also found that the effective work function enhancement by the AlNx interfacial layer increased when the concentration of SiO2 in the gate dielectric was increased. Thus, the enhancement was minimal for HfO2 and maximum for SiO2. A model is proposed to explain these results and a bonding analysis is presented to support the proposed model.
Peaks separation of the nonlinear refraction and nonlinear absorption induced by external electric field
Authors: Guan Dongyi , Chen Zhenghao , Zhou Yueliang , Jin Kui-Juan , Yang Guozhen
Published: March 2006

To investigate the relation between the nonlinear susceptibility and the wavelength, Ag:BaTiO3 composite films were synthesized on MgO(100) substrates under different external electric fields using pulsed laser deposition. The nonlinear optical properties of the films were measured by z-scan in the wavelength of 355–650nm. It is found that with increasing the electric field, the peak of the nonlinear refraction index shifts to longer wavelength (redshift) and is separated from the peak of the nonlinear absorption. With the separation, the values of ∣Reχ(3)∕Imχ(3)∣ can be enhanced obviously.
Impact of aerosol indirect effect on surface temperature over East Asia
Authors: Huang Yan , Dickinson Robert E. , Chameides William L.
Published: March 2006

A regional coupled climate–chemistry–aerosol model is developed to examine the impacts of anthropogenic aerosols on surface temperature and precipitation over East Asia. Besides their direct and indirect reduction of short-wave solar radiation, the increased cloudiness and cloud liquid water generate a substantial downward positive long-wave surface forcing; consequently, nighttime temperature in winter increases by +0.7°C, and the diurnal temperature range decreases by −0.7°C averaged over the industrialized parts of China. Confidence in the simulated results is limited by uncertainties in model cloud physics. However, they are broadly consistent with the observed diurnal temperature range decrease as reported in China, suggesting that changes in downward long-wave radiation at the surface are important in understanding temperature changes from aerosols.
A dopamine transporter gene functional variant associated with cocaine abuse in a Brazilian sample
Authors: Guindalini Camila , Howard Mark , Haddley Kate , Laranjeira Ronaldo , Collier David , Ammar Nik , Craig Ian , O’Gara Colin , Bubb Vivian J. , Greenwood Tiffany , Kelsoe John , Asherson Phil , Murray Robin M. , Castelo Adauto , Quinn John P. , Vallada Homero , Breen Gerome
Published: March 2006

The dopamine (DA) transporter DAT1 is a major target bound by cocaine in brain. We examined the influence of functional genetic variants in DAT1 on cocaine addiction. Repeat polymorphisms, including a 30-bp variable-number tandem repeat (VNTR) in intron 8 (Int8 VNTR) with two common alleles, were genotyped in cocaine-dependent abusers (
n
= 699) and in controls with no past history of drug abuse (
n
= 866) from São Paulo, Brazil. Positive association was observed with allele 3 of the Int8 VNTR and cocaine abuse (allele odds ratio = 1.2, 95% confidence interval = 1.01–1.37,
P
= 0.036; 3/3 homozygote odds ratio = 1.45, 95% confidence interval = 1.18–1.78,
P
= 0.0008). Population stratification was assessed and did not affect the results. Haplotypic analyses using additional polymorphisms indicated that the Int8 VNTR is responsible for the observed association. Functional analyses in reporter–gene constructs, demonstrated that allele 3 mediates significant (
P
< 0.05) but small reduced expression compared with the “protective” allele 2. This difference increased when 1 and 10 μM cocaine was added to the cell culture (≈40% reduction of the 3 allele expression versus the 2 allele). The 3 allele also demonstrated ≈3-fold-increased expression over the 2 allele in response to KCl plus forskolin challenge. We demonstrate a robust association between cocaine dependence and a VNTR allele in
SLC6A3
, conferring a small but detectible effect, and we show that this VNTR may be functional. This study suggests that DAT1 gene variation may play a role in cocaine dependence etiology.