bluuebunny/crossref_metadata_2025 huggingface dataset:
Passage of cell-penetrating peptides across a human epithelial cell layer in vitro
Authors: LINDGREN Maria E. , HÄLLBRINK Mattias M. , ELMQUIST Anna M. , LANGEL Ülo
Published: January 2004

Cell barriers are essential for the maintenance and regulation of the microenvironments of the human body. Cell-penetrating peptides have simplified the delivery of bioactive cargoes across the plasma membrane. Here, the passage of three cell-penetrating peptides (transportan, the transportan analogue transportan 10, and penetratin) across a Caco-2 human colon cancer cell layer in vitro was investigated. The peptides were internalized into epithelial Caco-2 cells as visualized by indirect fluorescence microscopy and quantified by fluorimetry. Studies of peptide outflow from cells showed that the peptides were in equilibrium across the plasma membrane. The ability of the peptides to cross a Caco-2 cell layer was tested in a two-chambered model system. After 120 min, 7.0%, 2.8% and 0.6% of added transportan, transportan 10 and penetratin respectively was detected in the lower chamber. Both transportan and transportan 10 reversibly decreased the trans-epithelial electrical resistance of the barrier model, with minimum values after 60 min of 46% and 60% of control respectively. Penetratin did not affect the resistance of the cell layer to the same extent. Although transportan markedly increased the passage of ions, the paracellular flux of 4.4 kDa fluorescein-labelled dextran was limited. In conclusion, the results indicate that the transportan peptides pass the epithelial cell layer mainly by a mechanism involving a transcellular pathway.
Ribosome-inactivating protein and apoptosis: abrin causes cell death via mitochondrial pathway in Jurkat cells
Authors: NARAYANAN Sriram , SUROLIA Avadhesha , KARANDE Anjali A.
Published: January 2004

Abrin belongs to the type II family of ribosome-inactivating proteins comprising a galactose-binding B chain coupled with a toxic A chain through a single disulphide linkage. Apart from its RNA-N-glycosidase activity, another role that has been recently ascribed to abrin was the induction of apoptosis. Studies were undertaken to determine the kinetics of these two activities. In the present study, we report that the signal for apoptosis is triggered at a time point later than the inhibition of protein synthesis. This apoptotic pathway induced by abrin is caspase 3-dependent but caspase 8-independent and involves mitochondrial membrane potential damage and reactive oxygen species production. Overexpression of B-cell lymphocytic-leukaemia proto-oncogene 2 was found to block this apoptotic pathway.
Venom phospholipases A2 of bamboo viper (Trimeresurus stejnegeri): molecular characterization, geographic variations and evidence of multiple ancestries
Authors: TSAI Inn-Ho , WANG Ying-Ming , CHEN Yi-Hsuan , TSAI Tein-Shun , TU Ming-Chung
Published: January 2004

Phospholipases A2 (PLA2s) were purified from the Trimeresurus stejnegeri venom obtained from various localities in Taiwan and three provinces in China, by gel filtration followed by reversed-phase HPLC. The precise molecular mass and N-terminal sequence of each PLA2 were determined. In addition to the six previously documented PLA2 isoforms of this species, we identified ten novel isoforms. The venom gland cDNAs of individual specimens of the viper from four localities were used for PCR and subsequent cloning of the PLA2s. The molecular masses and partial sequences of most of the purified PLA2s matched with those deduced from a total of 13 distinct cDNA sequences of these clones. Besides the commonly known Asp49 or Lys-49 PLA2s of crotalid venoms, a novel type of PLA2 with Asn-49 substitution at the Ca2+-binding site was discovered. This type of PLA2 is non-catalytic, but may cause local oedema and appears to be a venom marker of many tree vipers. In particular, we showed that T. stejnegeri displayed high geographic variations of the PLA2s within and between their Taiwanese and Chinese populations, which can be explained by geological isolation and prey ecology. A phylogenetic tree of the acidic venom PLA2s of this species and other related Asian vipers reveals that T. stejnegeri contains venom genes related to those from several sympatric pit vipers, including the genera Tropedolaemus and Gloydius besides the Trimeresurus itself. Taken together, these findings may explain the exceptionally high variations in the venom as well as the evolutionary advantage of this species.
Mutational analysis of the catalytic centre of the Citrobacter freundii AmpD N-acetylmuramyl-l-alanine amidase
Authors: GÉNÉREUX Catherine , DEHARENG Dominique , DEVREESE Bart , VAN BEEUMEN Jozef , FRÈRE Jean-Marie , JORIS Bernard
Published: January 2004

Citrobacter freundii AmpD is an intracellular 1,6-anhydro-N-acetylmuramyl-l-alanine amidase involved in both peptidoglycan recycling and β-lactamase induction. AmpD exhibits a strict specificity for 1,6-anhydromuropeptides and requires zinc for enzymic activity. The AmpD three-dimensional structure exhibits a fold similar to that of another Zn2+N-acetylmuramyl-l-alanine amidase, the T7 lysozyme, and these two enzymes define a new family of Zn-amidases which can be related to the eukaryotic PGRP (peptidoglycan-recognition protein) domains. In an attempt to assign the different zinc ligands and to probe the catalytic mechanism of AmpD amidase, molecular modelling based on the NMR structure and site-directed mutagenesis were performed. Mutation of the two residues presumed to act as zinc ligands into alanine (H34A and D164A) yielded inactive proteins which had also lost their ability to bind zinc. By contrast, the active H154N mutant retained the capacity to bind the metal ion. Three other residues which could be involved in the AmpD catalytic mechanism have been mutated (Y63F, E116A, K162H and K162Q). The E116A mutant was inactive, but on the basis of the molecular modelling this residue is not directly involved in the catalytic mechanism, but rather in the binding of the zinc by contributing to the correct orientation of His-34. The K162H and K162Q mutants retained very low activity (0.7 and 0.2% of the wild-type activity respectively), whereas the Y63F mutant showed 16% of the wild-type activity. These three latter mutants exhibited a good affinity for Zn ions and the substituted residues are probably involved in the binding of the substrate. We also describe a new method for generating the N-acetylglucosaminyl-1,6-anhydro-N-acetylmuramyl-tripeptide AmpD substrate from purified peptidoglycan by the combined action of two hydrolytic enzymes.
A role for palmitoylation in the quality control, assembly and secretion of apolipoprotein B
Authors: VILAS Gonzalo L. , BERTHIAUME Luc G.
Published: January 2004

ApoB (apolipoprotein B)-containing lipoprotein particles, such as chylomicrons, very-low-density and low-density lipoprotein particles, transport triacylglycerol and cholesteryl esters in the bloodstream. A palmitoylation site was previously mapped to Cys-1085 in a functional truncated apoB variant (apoB-29) and abolished by mutagenesis. This Cys-1085Ser mutation resulted in secretion of smaller and denser lipoprotein particles containing 80% less cholesteryl ester and triacylglycerol than wild-type controls. We show that palmitoylation of apoB-29 occurs in the ER (endoplasmic reticulum), stimulates the ER–Golgi transport rate of apoB-29 almost 2-fold, doubles the secretion efficiency of wild-type apoB-29 in comparison with (Cys-1085Ser)apoB-29 and reduces significantly the association of wild-type apoB-29 with calnexin in comparison with (Cys-1085Ser)apoB-29. While non-palmitoylated apoB-29 co-localized extensively with constitutively secreted transferrin, wild-type apoB-29 did so only partially and was enriched in ER extensions. Our results suggest that palmitoylation of apoB regulates the biogenesis of nascent apoB-containing lipoprotein particles by concentrating apoB in a specialized ER compartment and by stimulating dissociation from constituents of the ER quality-control machinery. This reduced interaction would lead to a faster ER–Golgi transit time and a higher secretion efficiency of wild-type apoB-29. Palmitoylation could regulate the amount of apoB available for secretion of neutral lipids.
Cytoskeletal protein 4.1G binds to the third intracellular loop of the A1 adenosine receptor and inhibits receptor action
Authors: LU Dongcheng , YAN Henglin , OTHMAN Timothy , TURNER Christopher P. , WOOLF Thomas , RIVKEES Scott A.
Published: January 2004

To identify binding partners of the A1AR (A1 adenosine receptor), yeast two-hybrid screening of a rat embryonic cDNA library was performed. This procedure led to the identification of erythrocyte membrane cytoskeletal protein (represented as 4.1G) as an A1AR-binding partner. Truncation studies revealed that the C-terminal domain of 4.1G was essential for binding to A1ARs and that the C-terminal domain of 4.1G and the third intracellular loop of A1ARs interacted. A1AR–4.1G interaction was also confirmed in studies using brain tissue. Studies in HEK-293 (human embryonic kidney 293) cells and Chinese-hamster ovary cells showed that 4.1G interfered with A1AR signal transduction, as 4.1G reduced A1AR-mediated inhibition of cAMP accumulation and intracellular calcium release. 4.1G also altered cell-surface A1AR expression. These observations identify 4.1G as a novel A1AR-binding partner that can regulate adenosine action.
Clathrin-dependent endocytosis
Authors: MOUSAVI Seyed Ali , MALERØD Lene , BERG Trond , KJEKEN Rune
Published: January 2004

The process by which clathrin-coated vesicles are produced involves interactions of multifunctional adaptor proteins with the plasma membrane, as well as with clathrin and several accessory proteins and phosphoinositides. Here we review recent findings highlighting new insights into mechanisms underlying clathrin-dependent endocytosis.
Identification of C-terminal motifs responsible for transmission of inhibition by ATP of mammalian phosphofructokinase, and their contribution to other allosteric effects
Authors: MARTÍNEZ-COSTA Oscar H. , HERMIDA Carmen , SÁNCHEZ-MARTÍNEZ Cristina , SANTAMARÍA Belén , ARAGÓN Juan J.
Published: January 2004

Systematic deletions and point mutations in the C-terminal extension of mammalian PFK (phosphofructokinase) led us to identify Leu-767 and Glu-768 of the M-type isoform (PFK-M) as the motifs responsible for the role of this region in inhibition by MgATP. These amino acids are the only residues of the C-terminus that are conserved in all mammalian isoforms, and were found to have a similar function in the C-type isoenzyme. Both residues in PFK-C and Leu-767 in PFK-M were also observed to be critical for inhibition by citrate, which is synergistic with that by MgATP. Binding studies utilizing titration of intrinsic protein fluorescence indicated that the C-terminal part of the enzyme participates in the signal transduction route from the MgATP inhibitory site to the catalytic site, but does not contribute to the binding of this inhibitor, whereas it is essential for the binding of citrate. Mutations of the identified structural motifs did not alter either the action of other allosteric effectors that also interact with MgATP, such as the inhibitor phosphoenolpyruvate and the strong activator fructose 2,6-bisphosphate, or the co-operative effect of fructose 6-phosphate. The latter data provide evidence that activation by fructose 2,6-bisphosphate and fructose 6-phosphate co-operativity are not linked to the same allosteric transition as that mediating inhibition by MgATP.
Targeting of skeletal muscle in vitro using biotinylated immunoliposomes
Authors: SCHNYDER Anita , KRÄHENBÜHL Stefan , TÖRÖK Michael , DREWE Jürgen , HUWYLER Jörg
Published: January 2004

In the present study, a non-covalent (biotin–streptavidin) coupling procedure for the preparation of pegylated immunoliposomes is presented, which simplifies the attachment of targeting vectors to sterically stabilized liposomes. A biotinylated poly(ethylene glycol) (PEG)-phospholipid [bio-PEG-distearoylphosphatidylethanolamine (DSPE)] was used as a linker between a streptavidin-conjugated monoclonal antibody (mAb) (i.e. the OX26 mAb raised against the rat transferrin receptor) and 150 nm liposomes. OX26–streptavidin had a biotin binding capacity of two to three biotin molecules per OX26–streptavidin conjugate. Immunostaining experiments with the OX26 mAb followed by fluorescent confocal microscopy revealed immunofluorescence labelling of the transferrin receptor on skeletal muscle, as well as in L6 cells, a continuous cell line derived from rat skeletal muscle. Uptake experiments with L6 cells using the OX26 mAb, fluorescence-labelled OX26–streptavidin or fluorescent OX26-immunoliposomes demonstrated cellular uptake and accumulation within an intracellular compartment of the OX26 mAb and its conjugates. Cellular uptake of OX26 conjugates was sensitive to competition with free OX26 antibody. In summary, these studies describe the design of biotinylated immunoliposomes as a universal drug transport vector and their potential for targeting of the transferrin receptor of skeletal muscle.
Murine bubblegum orthologue is a microsomal very long-chain acyl-CoA synthetase
Authors: FRAISL Peter , FORSS-PETTER Sonja , ZIGMAN Mihaela , BERGER Johannes
Published: January 2004

It has been suggested that a gene termed bubblegum (Bgm), encoding an acyl-CoA synthetase, could be involved in the pathogenesis of the inherited neurodegenerative disorder X-ALD (X-linked adrenoleukodystrophy). The precise function of the ALDP (ALD protein) still remains unclear. Aldp deficiency in mammals and Bgm deficiency in Drosophila led to accumulation of VLCFAs (very long-chain fatty acids). As a first step towards studying this interaction in wild-type versus Aldp-deficient mice, we analysed the expression pattern of the murine orthologue of the Bgm gene. In contrast with the ubiquitously expressed Ald gene, Bgm expression is restricted to the tissues that are affected by X-ALD such as brain, testis and adrenals. During mouse brain development, Bgm mRNA was first detected by Northern-blot analysis on embryonic day 18 and increased steadily towards adulthood, whereas the highest level of Ald mRNA was found on embryonic day 12 and decreased gradually during differentiation. Protein fractionation and confocal laser imaging of Bgm–green fluorescent protein fusion proteins revealed a microsomal localization that was different from peroxisomes (where Aldp is detected), endoplasmic reticulum and Golgi. Mouse Bgm showed acyl-CoA synthetase activity towards a VLCFA substrate in addition to LCFAs, and this activity was enriched in the microsomal compartment. Speculating that Bgm expression could be regulated by Ald deficiency, we compared the abundance of Bgm mRNA in wild-type and Ald knockout mice but observed no difference. Although mouse Bgm is capable of activating VLCFA, we conclude that a direct interaction between the mouse Bgm and the Aldp seems unlikely.
Induction of murine NAD(P)H:quinone oxidoreductase by 2,3,7,8-tetrachlorodibenzo-p-dioxin requires the CNC (cap n collar) basic leucine zipper transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2): cross-interaction between AhR (aryl hydrocarbon receptor) and Nrf2 signal transduction
Authors: MA Qiang , KINNEER Krista , BI Yongyi , CHAN Jefferson Y. , KAN Yuet Wai
Published: January 2004

TCDD (2,3,7,8-tetrachlorodibenzo-p-dixoin) induces phase II drug-metabolizing enzyme NQO1 [NAD(P)H:quinone oxidoreductase; EC 1.6.99.2; DT-diaphorase] in a wide range of mammalian tissues and cells. Here, we analysed the molecular pathway mediating NQO1 induction by TCDD in mouse hepatoma cells. Inhibition of protein synthesis with CHX (cycloheximide) completely blocks induction of NQO1 by TCDD as well as the basal expression and induction by phenolic antioxidant tBHQ (2-t-butylbenzene-1,4-diol), implicating a labile factor in NQO1 mRNA expression. The inhibition is both time- and concentration-dependent, requires inhibition of protein synthesis, and occurs at a transcriptional level. Inhibition of NQO1 transcription by CHX correlates with a rapid reduction of the CNC bZip (cap ‘n’ collar basic leucine zipper) transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2) through the 26 S proteasome pathway. Moreover, blocking Nrf2 degradation with proteasome inhibitor MG132 increases the amount of Nrf2 and superinduces NQO1 in the presence of TCDD or tBHQ. Finally, genetic experiments using AhR (aryl hydrocarbon receptor)-, Arnt (aryl hydrocarbon receptor nuclear translocator)- or Nrf2-deficient cells reveal that, while induction of NQO1 by TCDD depends on the presence of AhR and Arnt, the basal and inducible expression of NQO1 by either TCDD or tBHQ requires functional Nrf2. The findings demonstrate a novel role of Nrf2 in the induction of NQO1 by TCDD and provide new insights into the mechanism by which Nrf2 regulates the induction of phase II enzymes by both phenolic antioxidants and AhR ligands.
Reaction mechanism of chitobiose phosphorylase from Vibrio proteolyticus: identification of family 36 glycosyltransferase in Vibrio
Authors: HONDA Yuji , KITAOKA Motomitsu , HAYASHI Kiyoshi
Published: January 2004

A family 36 glycosyltransferase gene was cloned from Vibrio proteolyticus. The deduced amino acid sequence showed a high degree of identity with ChBP (chitobiose phosphorylase) from another species, Vibrio furnissii. The recombinant enzyme catalysed the reversible phosphorolysis of (GlcNAc)2 (chitobiose) to form 2-acetamide-2-deoxy-α-d-glucose 1-phosphate [GlcNAc-1-P] and GlcNAc, but showed no activity on cellobiose, indicating that the enzyme was ChBP, not cellobiose phosphorylase. In the synthetic reaction, the ChBP was active with α-d-glucose 1-phosphate as the donor substrate as well as GlcNAc-1-P to produce β-d-glucosyl-(1→4)-2-acetamide-2-deoxy-d-glucose with GlcNAc as the acceptor substrate. The enzyme allowed aryl-β-glycosides of GlcNAc as the acceptor substrate with 10–20% activities of GlcNAc. Kinetic parameters of (GlcNAc)2 in the phosphorolysis and GlcNAc-1-P in the synthetic reaction were determined as follows: phosphorolysis, k0=5.5 s−1, Km=2.0 mM; synthetic reaction, k0=10 s−1, Km=14 mM, respectively. The mechanism of the phosphorolytic reaction followed a sequential Bi Bi mechanism, as frequently observed with cellobiose phosphorylases. Substrate inhibition by GlcNAc was observed in the synthetic reaction. The enzyme was considered a unique biocatalyst for glycosidation.
Structure-function analysis of HKE4, a member of the new LIV-1 subfamily of zinc transporters
Authors: TAYLOR Kathryn M. , MORGAN Helen E. , JOHNSON Andrea , NICHOLSON Robert I.
Published: January 2004

The KE4 proteins are an emerging group of proteins with little known functional data. In the present study, we report the first characterization of the recombinant human KE4 protein in mammalian cells. The KE4 sequences are included in the subfamily of ZIP (Zrt-, Irt-like Proteins) zinc transporters, which we have termed LZT (LIV-1 subfamily of ZIP zinc Transporters). All these LZT sequences contain similarities to ZIP transporters, including the consensus sequence in transmembrane domain IV, which is essential for zinc transport. However, the new LZT subfamily can be separated from other ZIP transporters by the presence of a highly conserved potential metalloprotease motif (HEXPHEXGD) in transmembrane domain V. Here we report the location of HKE4 on intracellular membranes, including the endoplasmic reticulum, and its ability to increase the intracellular free zinc as measured with the zinc-specific fluorescent dye, Newport Green, in a time-, temperature- and concentration-dependent manner. This is in contrast with the zinc influx ability of another LZT protein, LIV-1, which was due to its plasma membrane location. Therefore we have added to the functionality of LZT proteins by reporting their ability to increase intracellular-free zinc, whether they are located on the plasma membrane or on intracellular membranes. This result, in combination with the crucial role that zinc plays in cell growth, emphasizes the importance of this new LZT subfamily, including the KE4 sequences, in the control of intracellular zinc homoeostasis, aberrations of which can lead to diseases such as cancer, immunological disorders and neurological dysfunction.
Coagulation factor Va Glu-96-Asp-111: a chelator-sensitive site involved in function and subunit association
Authors: ZEIBDAWI Abed R. , GRUNDY Jean E. , LASIA Bogna , PRYZDIAL Edward L. G.
Published: January 2004

Coagulation FVa (factor Va) accelerates the essential generation of thrombin by FXa (factor Xa). Although the noncovalent Ca2+-dependent association between the FVa light and heavy subunits (FVaL and FVaH) is required for function, little is known about the specific residues involved. Previous fragmentation studies and homology modelling led us to investigate the contribution of Leu-94–Asp-112. Including prospective divalent cation-binding acidic amino acids, nine conserved residues were individually replaced with Ala in the recombinant B-domainless FVa precursor (ΔFV). While mutation of Thr-104, Glu-108, Asp-112 or Tyr-100 resulted in only minor changes to FXa-mediated thrombin generation, the functions of E96A (81%), D111A (70%) and D102A (60%) mutants (where the single-letter amino acid code is used) were notably reduced. The mutants targeting neighbouring acidic residues, Asp-79 and Glu-119, had activity comparable with ΔFV, supporting the specific involvement of select residues. Providing a basis for reduced activity, thrombin treatment of D111A resulted in spontaneous dissociation of subunits. Since FVaH and FVaL derived from E96A or D102A remained associated in the presence of Ca2+, like the wild type, but conversely dissociated rapidly upon chelation, a subtle difference in divalent cation co-ordination is implied. Subunit interactions for all other single-point mutants resembled the wild type. These data, along with corroborating multipoint mutants, reveal Asp-111 as essential for FVa subunit association. Although Glu-96 and Asp-102 can be mutated without gross changes to divalent cation-dependent FVaH–FVaL interactions, they too are required for optimal function. Thus Glu-96–Asp-111 imparts at least two discernible effects on FVa coagulation activity.
Size-dependent internalization of particles via the pathways of clathrin- and caveolae-mediated endocytosis
Authors: REJMAN Joanna , OBERLE Volker , ZUHORN Inge S. , HOEKSTRA Dick
Published: January 2004

Non-phagocytic eukaryotic cells can internalize particles <1 µm in size, encompassing pathogens, liposomes for drug delivery or lipoplexes applied in gene delivery. In the present study, we have investigated the effect of particle size on the pathway of entry and subsequent intracellular fate in non-phagocytic B16 cells, using a range of fluorescent latex beads of defined sizes (50–1000 nm). Our data reveal that particles as large as 500 nm were internalized by cells via an energy-dependent process. With an increase in size (50–500 nm), cholesterol depletion increased the efficiency of inhibition of uptake. The processing of the smaller particles was significantly perturbed upon microtubule disruption, while displaying a negligible effect on that of the 500 nm beads. Inhibitor and co-localization studies revealed that the mechanism by which the beads were internalized, and their subsequent intracellular routing, was strongly dependent on particle size. Internalization of microspheres with a diameter <200 nm involved clathrin-coated pits. With increasing size, a shift to a mechanism that relied on caveolae-mediated internalization became apparent, which became the predominant pathway of entry for particles of 500 nm in size. At these conditions, delivery to the lysosomes was no longer apparent. The data indicate that the size itself of (ligand-devoid) particles can determine the pathway of entry. The clathrin-mediated pathway of endocytosis shows an upper size limit for internalization of approx. 200 nm, and kinetic parameters may determine the almost exclusive internalization of such particles along this pathway rather than via caveolae.
Further evidence that the tyrosine phosphorylation of glycogen synthase kinase-3 (GSK3) in mammalian cells is an autophosphorylation event
Authors: COLE Adam , FRAME Sheelagh , COHEN Philip
Published: January 2004

Phosphorylation of the endogenous GSK3α (glycogen synthase kinase-3α) at Tyr279 and GSK3β at Tyr216 was suppressed in HEK-293 or SH-SY5Y cells by incubation with pharmacological inhibitors of GSK3, but not by an Src-family inhibitor, 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2), or a general protein tyrosine kinase inhibitor (genistein). GSK3β transfected into HEK-293 cells or Escherichia coli became phosphorylated at Tyr216, but catalytically inactive mutants did not. GSK3β expressed in insect Sf 21 cells or E. coli was extensively phosphorylated at Tyr216, but the few molecules lacking phosphate at this position could autophosphorylate at Tyr216in vitro after incubation with MgATP. The rate of autophosphorylation was unaffected by dilution and was suppressed by the GSK3 inhibitor kenpaullone. Wild-type GSK3β was unable to catalyse the tyrosine phosphorylation of catalytically inactive GSK3β lacking phosphate at Tyr216. Our results indicate that the tyrosine phosphorylation of GSK3 is an intramolecular autophosphorylation event in the cells that we have studied and that this modification enhances the stability of the enzyme.
Putative role of membranes in the HIV fusion inhibitor enfuvirtide mode of action at the molecular level
Authors: VEIGA Salomé , HENRIQUES Sónia , SANTOS Nuno C. , CASTANHO Miguel
Published: January 2004

Partition of the intrinsically fluorescent HIV fusion inhibitor enfuvirtide into lipidic membranes is relatively high (ΔG=6.6 kcal·mol−1) and modulated by cholesterol. A shallow position in the lipidic matrix makes it readily available for interaction with gp41. No conformational energetic barrier prevents enfuvirtide from being active in both aqueous solution and lipidic membranes. Lipidic membranes may play a key role in the enfuvirtide biochemical mode of action.
Secrets of insulin and IGF-1 regulation of insulin secretion revealed
Authors: SHEPHERD Peter R.
Published: January 2004

There has been ongoing controversy over the respective roles of insulin-like growth factor-1 receptors and insulin receptors in controlling insulin release from β-cells of the pancreas. An acute knock-down experiment exploiting small interfering RNA approaches provides a resolution: both are required.
Diagnosis of periodontal manifestations of systemic diseases
Authors: Jordan Richard C. K.
Published: January 2004

Many systemic diseases can mimic periodontitis or gingivitis. These include many immunologic, infectious, neoplastic and metabolic disorders. In comparison with periodontitis and gingivitis, these disorders are considerably less common. However, since their diagnosis and management differ, a high index of suspicion is frequently needed when confronted a patient presenting with gingival or periodontal disease. This chapter has reviewed a number of systemic conditions that may mimic clinically both gingivitis and chronic periodontitis and has focused on the features that may assist the clinician in making the diagnosis and providing specific therapies.
Electrophysiology of inducible atrial flutter in patients with atrioventricular nodal reentrant tachycardia
Authors: Liu Shaowen , Yuan Shiwen , Hertervig Eva , Kongstad Ole , Ljungstrom Erik , Bertil Olsson S.
Published: January 2004

An association between atrial flutter and atrioventricular nodal reentrant tachycardia (AVNRT) has been observed, but the underlying mechanisms are poorly defined. This issue was therefore investigated by comparing the electrophysiological properties of AVNRT patients with and without inducible atrial flutter and those of patients with a history of flutter. Twenty‐nine patients with clinically documented atrial flutter and 104 with AVNRT were studied. Atrial flutter was induced in 38 (37%) AVNRT patients during standardized electrophysiological testing before radiofrequency ablation. The atrial relative refractory periods in AVNRT patients with inducible flutter (260 ± 30 ms) were significantly shorter than those of either patients with a history of flutter (282 ± 30 ms; P = 0·02) or AVNRT patients without inducible flutter (284 ± 38 ms; P = 0·006). The atrial effective refractory periods in AVNRT patients with inducible flutter (205 ± 31 ms) were shorter than in AVNRT patients without inducible flutter (227 ± 40 ms; P = 0·01). The maximum AH interval during premature atrial stimulation in patients with clinical flutter (239 ± 94 ms) was shorter than in AVNRT patients either with (290 ± 91 ms; P = 0·04) or without inducible flutter (313 ± 101 ms; P = 0·002). However, no significant differences were found in the maximum AH interval achieved during incremental atrial pacing among different groups. Our data show that a non‐clinical flutter could more often be induced in those who had short atrial refractoriness. Despite their anatomical proximity, the slow pathway conduction of AVNRT and the isthmus slow conduction of flutter may be related to different mechanisms.
Electromyographic signs of neuromuscular fatigue are concomitant with further increase in ventilation during static handgrip
Authors: Hug F. , Faucher M. , Marqueste T. , Guillot Ch. , Kipson N. , Jammes Y.
Published: January 2004

We questioned if a non‐linear increase in ventilation defining a ventilatory threshold (VTh) accompanied the electromyographic (EMG) signs of neuromuscular fatigue. Indeed, the intramuscular accumulation of metabolites may activate the afferent nervous pathways responsible for both the ‘muscle wisdom’ phenomenon and the respiratory centre activation. During inframaximal (50%) handgrip sustained until exhaustion, minute ventilation (VE), VE/Vo2 and VE/Vco2 ratios were measured simultaneously with surface EMG of the ‘flexor digitorum’ muscle. VTh was defined as a non‐linear VE increase and/or an abrupt VE/Vo2 increase without any concomitant increase in the VE/Vco2 ratio. Handgrip was repeated during complete arterial blood flow interruption in order to suppress any venous return from the exercising forearm. In both control and blood flow interruption conditions, an abrupt increase in the VE/Vo2 ratio was measured in the majority of trials (13 of 15 and 14 of 15, respectively) and the EMG signs of neuromuscular fatigue (a decline in median frequency and/or a non‐linear increase in low‐frequency EMG energies, EL) were concomitant with the VTh determination. Thus, VTh occurs during sustained static contraction and is concomitant with EMG signs of neuromuscular fatigue. Neurogenic factors seem to be responsible for the two responses which persist despite the absence of any release of metabolites in the circulation.
Assessment of 99mTc‐sestamibi myocardial redistribution following acute myocardial infarction and revascularization
Authors: Kaltoft Anne , Bøttcher Morten , Rehling Michael
Published: January 2004

Revascularization with primary percutaneous coronary intervention for ST segment elevation myocardial infarction results in restored epicardial flow in the majority of patients. However, in more than 25% of patients, flow does not translate into tissue perfusion. To assess revascularization success, it is necessary to evaluate beyond epicardial flow and to address tissue perfusion. 99mTc‐sestamibi single photon emission computed tomography (SPECT) might be useful in this setting, but whether sestamibi redistributes when administered during reperfusion has been debated. The aim of this study was to investigate whether clinically significant redistribution could be detected in a porcine model mimicking acute myocardial infarction and revascularization. Ten pigs were studied in a closed‐chest model of myocardial infarction. 99mTc‐sestamibi was administered during reperfusion, and SPECT was performed every 30 min for 4 h. The quantitative program CEQUAL was used for analysis and perfusion defects were reported in percentage. All animals had eight acquisitions. The size of the perfusion defect in the individual animals ranged from (mean ± SD) 13 ± 3 to 34 ± 2%. The difference between the first and the last perfusion defect in a single animal was (mean ± SD) 2·5 ± 5·3%, which is not statistically significant (P = 0·17). The slopes of regression lines obtained from plots of the individual values ranged from −1·39 to 0·76 with a mean of −0·23 ± 0·68, which is not statistically significant (P = 0·31). In conclusion, we found no sign of sestamibi redistribution in this experimental set‐up of reperfused myocardial infarction. If these findings can be extrapolated to clinical practice, then it means that acquisition can be performed at any time within the first 4 h after tracer injection without significant difference in perfusion assessment.
Peripheral pulse pressure responses to postural stress do not reflect those at the carotid artery
Authors: Steinback Craig D. , O'Leary Deborah D. , Wang Simon S. , Kevin Shoemaker J.
Published: January 2004

Objective:  Interpretation of baroreflex cardiovascular control requires accurate assessment of pulse pressure (PP) in central arteries under conditions of varying systemic or hydrostatic pressure. The objective of this study was to examine whether changes in PP during postural stress were similar in the peripheral versus carotid arteries.

Design:  Protocol A: Pulse pressure was measured in both the left (Millar tonometer) and right (Colin Pilot) radial arteries, and in the finger (Finapres) in seated subjects (n = 7) who performed Valsalva's manoeuvre. Protocol B: PP was measured from the carotid (Millar tonometer), and from the finger and wrist kept at the level of the carotid artery, during supine and 60° head‐up postures.

Results:  Protocol A: Pulse pressures during Valsalva's manoeuvre were highly correlated between all devices (r = 0·6–0·8). Protocol B: compared with supine, PP was reduced in both the finger and wrist during head‐up‐tilt (HUT) (P<0·05), but not in the carotid artery.

Conclusions:  During Valsalva manoeuvers the Millar and Colin tonometers similarly tracked PP over a wide range of rapidly changing pressures. This observation provided confidence for the further use of the hand‐held device for central measurements during changes in posture. The results from Protocol B indicate that peripheral PP measurements are not suitable surrogates for carotid pulse pressures during HUT.
Estimate of pulmonary diffusing capacity for oxygen during exercise in humans from routine O2 and CO2 measurements
Authors: Vidal Melo M. F. , Barazanji K. , Winga E. , Johnson R. L.
Published: January 2004

A method to estimate pulmonary diffusing capacity for O2 (DLo2) during exercise based on routine O2 and CO2 transport variables is presented. It is based on the fitting of a mathematical model to gas exchange data. The model includes heterogeneity (described as two exchanging compartments), diffusion limitation and right‐to‐left shunt. Mass conservation equations and Bohr integration were solved to calculate partial pressures in each compartment. Diffusion was distributed with perfusion. Two‐compartment ventilation and perfusion distributions were estimated at rest during conditions of negligible diffusion limitation. These distributions were used during hypoxic and normoxic exercise to obtain the DLo2 from the model computations (DLo22C) compatible with experimental data. Three normals, four sarcoid patients and four patients after lung resection were studied. An independent technique for carbon monoxide was used to provide experimental estimates of DLo2 (DLo2EXP, rebreathing technique for sarcoid patients and single breath for lung resection). DLo22C was highly correlated with DLo2EXP (r2 = 0·95, P<0·001) and the slope of the regression line was not statistically different from 1. The mean (DLo2EXP − DLo22C) difference was −1·0 ± 7·4 ml min−1 mmHg−1. The results suggest that use of a refined analytical procedure allows for assessment of DLo2 from routine O2 and CO2 measurements comparable with those obtained from independent carbon monoxide techniques. The method may be an alternative for estimates of DLo2 during exercise.
Regional ventilation and distribution of emphysema – a quantitative comparison
Authors: Johansson Åke , Vikgren Jenny , Moonen Michaela , Tylén Ulf , Bake Björn
Published: January 2004

The distribution of ventilation and emphysema throughout the lung was compared in 20 emphysematous patients who were candidates for lung volume reduction surgery. Ventilation distribution among 1·6‐cm‐high stripe regions was obtained in supine position by planar gamma camera scintigraphy after inhalation of technegas®. Results from nine healthy subjects provided normal stripe count rates. Patient count rates were expressed as the difference from predicted normal stripe count rate (ΔSVI). Thus, ΔSVI is a relative index of abnormal ventilation. Emphysema was assessed quantitatively by a density mask method on corresponding slices of high resolution computed tomography (HRCT). The results show that in the majority of patients, there is a highly significant relationship between the degree of stripe hypoventilation and the amount of distribution of emphysema, but in some patients no such relationship is found. We speculate that the distribution of airway obstruction not necessarily follows the distribution of emphysema, which could explain the lack of concordance between ventilation and emphysema distribution in some patients. We conclude that ventilation scintigraphy contains complementary information to lung HRCT.
Charge trapping studies on ultrathin ZrO2 and HfO2 high-k dielectrics grown by room temperature ultraviolet ozone oxidation
Authors: Ramanathan Shriram , McIntyre Paul C. , Guha Supratik , Gusev Evgeni
Published: January 2004

We report detailed charge trapping reliability characteristics of ultrathin ZrO2 and HfO2 dielectrics grown by the ultraviolet ozone oxidation (UVO) method. We also discuss the dependence of charge trapping on the top electrode deposition process, specifically in situ versus ex situ processed gates. Electrical data show that the charge trapping characteristics depend on the deposition method for the top electrode, likely due to exposure of the high-k material to ambient prior to deposition of the electrode. It is also shown that C–V hysteresis is not a complete measure of the charge trapping characteristics of the dielectrics.
Stress and structural relaxation in amorphous hydrogenated carbon films
Authors: Lejeune M. , Benlahsen M. , Bouzerar R.
Published: January 2004

The correlation between the residual stress and the atomic-bond structure has been investigated in detail in hydrogenated amorphous films (a-C:H). The relaxation process was studied in relation with the Raman characteristics evolution and the induced metric distortions during growth. The analysis of the Raman data shows that the metric distortions alone cannot explain the stress relaxation in the deposited films. The creation of some topological defects, such as odd rings, is required to explain both the Raman features behavior and the structural relaxation in the a-C:H samples.
Dynamics of trapped charge in GaN/AlGaN/GaN high electron mobility transistors grown by plasma-assisted molecular beam epitaxy
Authors: Mitrofanov Oleg , Manfra Michael
Published: January 2004

We report on the dynamics of trapped charge in unpassivated GaN/AlGaN/GaN high electron mobility transistors grown by plasma-assisted molecular beam epitaxy. Trap states are probed using a transient channel-current technique. By tailoring the gate pulse depth and width, this method allows selective probing of different trapping centers. We have identified at least two different trap centers that influence the current dynamics in our structures. In addition, the charge emission from the faster trap is found to have a clear square-root dependence on the applied electric field. This unambiguous field dependence allows us to isolate the mechanisms responsible for emission. We also identify the trapping mechanism and estimate the characteristic time required to fill available trap states and a lower bound for the trap density.
Discrete wavelength tunable laser using microelectromechanical systems technology
Authors: Zhang X. M. , Liu A. Q. , Tang D. Y. , Lu C.
Published: January 2004

A discrete wavelength tunable laser has been demonstrated using microelectromechanical systems (MEMS) technology. The laser system is formed by integrating a semiconductor laser, a single-mode optical fiber, and a MEMS mirror onto a single chip. It has overall dimensions of 1.5 mm×1 mm×0.6 mm (not including the optical fiber), and can be tuned to sweep a wavelength range of 13.5 nm within 1 ms. Unlike the conventional continuously tunable lasers, the laser system enables discrete wavelength tuning by making use of a short external cavity and weak feedback.
The vibrational properties of one-dimensional ZnO:Ce nanostructures
Authors: Cheng Baochang , Xiao Yanhe , Wu Guosheng , Zhang Lide
Published: January 2004

Different morphological one-dimensional ZnO:Ce nanostructures were synthesized on a large scale. The microstructures and vibrational properties were investigated by x-ray diffraction, electron microscopy, Raman spectroscopy, and infrared spectroscopy. The results show that Ce can effectively control the growth of ZnO nanostructures. The change of the morphology and local structure of ZnO under the influence of Ce results in the variation of vibrational properties. In Raman spectra of doped samples, some classical modes, such as A1 and E1 modes, disappear, and two anomalous modes at 527 and 667 cm−1 are observed, whose intensity decreases with the increase of synthesis temperature. In infrared spectra, some surface phonon modes appear. Compared with those of the undoped sample, all the normal modes observed in the Ce-doped samples blueshift, and the extent of the blueshift decreases with increasing synthesis temperature in the Raman and infrared spectra.
Low-noise photon counting with a radio-frequency quantum-dot field-effect transistor
Authors: Kardynał B. E. , Shields A. J. , Beattie N. S. , Farrer I. , Cooper K. , Ritchie D. A.
Published: January 2004

We present photon counting experiments with a single-photon detector based on a field-effect transistor gated by a layer of InAs quantum dots. A cryogenic radio-frequency amplifier is used to convert the photon-induced steps in the source-drain current of the transistor into voltage peaks. We measure a maximum photon detection efficiency of 0.14%, corresponding to internal quantum efficiency of 10%. The dark count rate is less than 10−8 ns−1 when the efficiency is 0.045%.
Effective broadband detection of nanometer laser-induced ultrasonic surface displacements by CdTe:V adaptive photoelectromotive force detector
Authors: Stepanov S. , Rodrı́guez P. , Trivedi S. , Wang C.-C.
Published: January 2004

Results of experiments studying the utilization of adaptive CdTe:V photoelectromotive force (photo-EMF) detector for high-sensitivity broadband detection of laser-generated ultrasound are presented. Unlike widely used GaAs photo-EMF detectors, the devices used here demonstrate no significant electron-hole competition. This ensures effective detection of ≅1 nm surface displacements with ≅0.1 mW of the signal beam power in 10 MHz detection frequency band, even in simple transverse detector configuration. For the wavelength of λ=852 nm used in the experiments, the dielectric cutoff frequency of a typical device was approaching 1 MHz. This, in principle, enables monitoring of as-processed objects moving with in-plane velocities up to 10 m/s.
C
60
as a Faraday cage
Authors: Delaney P. , Greer J. C.
Published: January 2004

Endohedral fullerenes have been proposed for a number of technological uses, for example, as a nanoscale switch, memory bit and as qubits for quantum computation. For these technology applications, it is important to know the ease with which the endohedral atom can be manipulated using an applied electric field. We find that the Buckminsterfullerene (C60) acts effectively as a small Faraday cage, with only 25% of the field penetrating the interior of the molecule. Thus influencing the atom is difficult, but as a qubit the endohedral atom should be well shielded from environmental electrical noise. We also predict how the field penetration should increase with the fullerene radius.
Femtosecond-laser-encoded distributed-feedback color center laser in lithium fluoride single crystals
Authors: Kawamura Ken-ichi , Hirano Masahiro , Kurobori Toshio , Takamizu Daizyu , Kamiya Toshio , Hosono Hideo
Published: January 2004

Laser-active F2 centers were produced in lithium fluoride (LiF) at a concentration of 2×1018 cm−3 by irradiating focused femtosecond (fs) laser pulses from a mode-locked titanium sapphire laser (wavelength ∼800 nm, emission pulse duration ∼100 fs). This technique was used to write waveguides embedded in LiF crystals. A refractive index change estimated from a guide propagation method was approximately +1% at a wavelength of 633 nm. Refractive index-modulated volume-type gratings were also encoded inside LiF crystals by a single interfered fs laser pulse. The distributed feedback laser structure was fabricated using the gratings thus encoded, which exhibited a room-temperature F2-color center laser oscillation at 707 nm. This demonstrates a DFB color center laser operating at room temperature utilizing photon written, permanent Bragg gratings.
Near-diffraction-limited coherent emission from large aperture antiguided vertical-cavity surface-emitting laser arrays
Authors: Bao Ling , Kim Nam-Heon , Mawst Luke J. , Elkin N. N. , Troshchieva V. N. , Vysotsky D. V. , Napartovich A. P.
Published: January 2004

We demonstrate that in-phase mode operation with a near-diffraction-limited beam can be realized in large aperture (up to 100 elements) antiguided vertical-cavity surface-emitting laser (VCSEL) arrays. A selective etching process with two-step metalorganic chemical vapor deposition is used for fabrication of the antiguided VCSEL array structures. Modal discrimination is enhanced by intentionally choosing a GaAs cap thickness so as to introduce suitable loss to array interelement regions. Far field patterns indicate in-phase mode operation from both triangular and rectangular geometry antiguided VCSEL arrays, which is in good agreement with theory.
Light emission from a polymer transistor
Authors: Ahles Marcus , Hepp Aline , Schmechel Roland , von Seggern Heinz
Published: January 2004

We report on light emission from a polymeric transistor that utilizes interdigitated source and drain electrodes with channel length of 5 μm in a bottom gate configuration based on a Si/SiO2 substrate. The polymer investigated is poly[9,9-di(ethylhexyl)fluorene] deposited by spin coating from chloroform solution to achieve an active layer thickness of 40 nm. Light emission occurs above drain source voltages of −60 V and the light intensity can be controlled by the gate voltage. Emission occurs close to the drain electrode as determined by optical microscopy. The transistor operates in hole accumulation mode without saturation of the output characteristics.
Conformal thin-film silicon nitride deposited by hot-wire chemical vapor deposition
Authors: Wang Qi , Ward Scott , Gedvilas Lynn , Keyes Brian , Sanchez Errol , Wang Shulin
Published: January 2004

We have studied silicon nitride thin films deposited by hot-wire chemical vapor deposition as a function of the substrate temperature and hydrogen dilution. We found that adding H2 to the process significantly enhances silicon nitride film deposition. High-quality films can be grown at low substrate temperatures (<350 °C). At optimized conditions, a 500-Å-thick silicon nitride film gives a nearly 100% surface coverage on a 100 nm scale object. H dilution dramatically increases the NH2 radicals in the process and leads to conformal films.