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V Germain

Publications and source records attributed to V Germain.

At least 19 recordsLinked to original sources
PubMed2005

Mesostructures of cobalt nanocrystals. 2. Mechanism.

Mesoscopic patterns of cobalt nanocrystals produced by applying a magnetic field perpendicular to the substrate during the deposition process are presented. These mesoscopic patterns markedly differ with the size distribution of the cobalt nanocrystals. Well-defined columns are produced when the size distribution of cobalt nanocrystals is low; conversely, the coalescence of columns with formations of labyrinths occurs for a large size distribution. A formation mechanism of these structures is proposed.

Journal Article↗
PubMed2005

Mesostructures of cobalt nanocrystals. 1. Experiment and theory.

Solid mesostructures made of cylinders are produced by the slow evaporation of cobalt nanocrystals dispersed in hexane and subjected to an applied field perpendicular to the substrate. Varying the initial nanocrystal concentration is found to be an efficient method for changing the pattern size. The experimental structures and the theoretical predictions based on the minimization of the total free energy are in good agreement. A comparison of experiment with theory allowed us to conclude that the mesostructures form as a result of a liquid-gas phase transition during the evaporation process. Within the theoretical model and the experimental data, it is concluded that the phase ratio of the magnetic to the total volume and the height of the cylinders govern the pattern geometry. In contrast, because of the saturation of the magnetization curve, the mesostructures are not influenced by the field strength.

Journal Article↗
PubMed2005

Silver nanodisks: size selection via centrifugation and optical properties.

Silver nanodisks, having two different sizes, and spherical particles are synthesized by soft chemistry. By using centrifugation, nanodisks are mainly selected. The experimental absorption spectra of these nanodisks with different sizes are compared to those simulated using the discrete dipole approximation method. For small nanodisk sizes, the nanodisk shape is neglected and the simulated spectra closest to the experiments are obtained by assuming a spheroidal particle. Conversely, for larger nanodisks, the precise geometries represented by snip and aspect ratio are needed for good agreement between experiments and simulations.

Journal Article↗
PubMed2001

Requirement for 3-ketoacyl-CoA thiolase-2 in peroxisome development, fatty acid beta-oxidation and breakdown of triacylglycerol in lipid bodies of Arabidopsis seedlings.

3-ketoacyl-CoA thiolase (KAT) (EC: 2.3.1.16) catalyses a key step in fatty acid beta-oxidation. Expression of the Arabidopsis thaliana KAT gene on chromosome 2 (KAT2), which encodes a peroxisomal thiolase, is activated in early seedling growth. We identified a T-DNA insertion in this gene which abolishes its expression and eliminates most of the thiolase activity in seedlings. In the homozygous kat2 mutant, seedling growth is dependent upon exogenous sugar, and storage triacylglycerol (TAG) and lipid bodies persist in green cotyledons. The peroxisomes in cotyledons of kat2 seedlings are very large, the total peroxisomal compartment is dramatically increased, and some peroxisomes contain unusual membrane inclusions. The size and number of plastids and mitochondria are also modified. Long-chain (C16 to C20) fatty acyl-CoAs accumulate in kat2 seedlings, indicating that the mutant lacks long-chain thiolase activity. In addition, extracts from kat2 seedlings have significantly decreased activity with aceto-acetyl CoA, and KAT2 appears to be the only thiolase gene expressed at significant levels during germination and seedling growth, indicating that KAT2 has broad substrate specificity. The kat2 phenotype can be complemented by KAT2 or KAT5 cDNAs driven by the CaMV 35S promoter, showing that these enzymes are functionally equivalent, but that expression of the KAT5 gene in seedlings is too low for effective catabolism of TAG. By comparison with glyoxylate cycle mutants, it is concluded that while gluconeogenesis from fatty acids is not absolutely required to support Arabidopsis seedling growth, peroxisomal beta-oxidation is essential, which is in turn required for breakdown of TAG in lipid bodies.

Acetyl-CoA C-Acyltransferase↗
PubMed2000

Postgerminative growth and lipid catabolism in oilseeds lacking the glyoxylate cycle.

The glyoxylate cycle is regarded as essential for postgerminative growth and seedling establishment in oilseed plants. We have identified two allelic Arabidopsis mutants, icl-1 and icl-2, which lack the glyoxylate cycle because of the absence of the key enzyme isocitrate lyase. These mutants demonstrate that the glyoxylate cycle is not essential for germination. Furthermore, photosynthesis can compensate for the absence of the glyoxylate cycle during postgerminative growth, and only when light intensity or day length is decreased does seedling establishment become compromised. The provision of exogenous sugars can overcome this growth deficiency. The icl mutants also demonstrate that the glyoxylate cycle is important for seedling survival and recovery after prolonged dark conditions that approximate growth in nature. Surprisingly, despite their inability to catalyze the net conversion of acetate to carbohydrate, mutant seedlings are able to break down storage lipids. Results suggest that lipids can be used as a source of carbon for respiration in germinating oilseeds and that products of fatty acid catabolism can pass from the peroxisome to the mitochondrion independently of the glyoxylate cycle. However, an additional anaplerotic source of carbon is required for lipid breakdown and seedling establishment. This source can be provided by the glyoxylate cycle or, in its absence, by exogenous sucrose or photosynthesis.

Acetates↗
PubMed2000

Monosaccharide/proton symporter AtSTP1 plays a major role in uptake and response of Arabidopsis seeds and seedlings to sugars.

The aim of this study was to investigate the in vivo properties and function of the high-affinity monosaccharide/proton symporter AtSTP1 of Arabidopsis. We isolated an Atstp1 knock-out mutant and found that this plant grows and develops normally. The AtSTP1 gene is expressed in germinating seeds and seedlings, with AtSTP1 activity found mainly in the seedling root. The rate of uptake of [(14)C]-3-O-methylglucose and [(14)C]-D-glucose is 60% less in Atstp1 seedlings than in the wild type, showing that AtSTP1 is the major monosaccharide transporter in Arabidopsis seedlings. Transport of D-galactose and D-mannose is also up to 60% less in Atstp1 seedlings compared to wild type, but transport of D-fructose, L-arabinose and sucrose is not reduced. Germination of Atstp1 seed shows reduced sensitivity to D-mannose, demonstrating that AtSTP1 is active before germination. Atstp1 seedlings grow effectively on concentrations of D-galactose that inhibit wild-type growth, even at up to 100 mM D-galactose, indicating that active transport by AtSTP1 plays a major role at very high concentrations of exogenous sugar. These findings provide insight into the physiological function of AtSTP1 and clearly establish its importance in the uptake of extracellular sugars by the embryo and in seedlings.

Arabidopsis↗
PubMed1999

Tyrosine 319, a newly identified phosphorylation site of ZAP-70, plays a critical role in T cell antigen receptor signaling.

Following T cell antigen receptor (TCR) engagement, the protein tyrosine kinase (PTK) ZAP-70 is rapidly phosphorylated on several tyrosine residues, presumably by two mechanisms: an autophosphorylation and a trans-phosphorylation by the Src-family PTK Lck. These events have been implicated in both positive and negative regulation of ZAP-70 activity and in coupling this PTK to downstream signaling pathways in T cells. We show here that Tyr315 and Tyr319 in the interdomain B of ZAP-70 are autophosphorylated in vitro and become phosphorylated in vivo upon TCR triggering. Moreover, by mutational analysis, we demonstrate that phosphorylation of Tyr319 is required for the positive regulation of ZAP-70 function. Indeed, overexpression in Jurkat cells and in a murine T cell hybridoma of a ZAP-70 mutant in which Tyr319 was replaced by phenylalanine (ZAP-70-Y319F) dramatically impaired anti-TCR-induced activation of the nuclear factor of activated T cells and interleukin-2 production, respectively. Surprisingly, an analogous mutation of Tyr315 had little or no effect. The inhibitory effect of ZAP-70-Y319F correlated with a substantial loss of its activation-induced tyrosine phosphorylation and up-regulation of catalytic activity, as well as with a decreased in vivo capacity to phosphorylate known ZAP-70 substrates, such as SLP-76 and LAT. Collectively, our data reveal the pivotal role of Tyr319 phosphorylation in the positive regulation of ZAP-70 and in TCR-mediated signaling.

Amino Acid Sequence↗
PubMed1998

Anti-peptide antibodies detect conformational changes of the inter-SH2 domain of ZAP-70 due to binding to the zeta chain and to intramolecular interactions.

T cell receptor (TCR) triggering induces association of the protein tyrosine kinase ZAP-70, via its two src-homology 2 (SH2) domains, to di-phosphorylated Immunoreceptor Tyrosine-based Activation Motifs (2pY-ITAMs) present in the intracellular tail of the TCR-zeta chain. The crystal structure of the SH2 domains complexed with a 2pY-ITAM peptide suggests that the 60-amino acid-long inter-SH2 spacer helps the SH2 domains to interact with each other to create the binding site for the 2pY-ITAM. To investigate whether the inter-SH2 spacer has additional roles in the whole ZAP-70, we raised antibodies against two peptides of this region and probed ZAP-70 structure under various conditions. We show that the reactivity of antibodies directed at both sequences was dramatically augmented toward the tandem SH2 domains alone compared with that of the entire ZAP-70. This indicates that the conformation of the inter-SH2 spacer is not maintained autonomously but is controlled by sequences C-terminal to the SH2 domains, namely, the linker region and/or the kinase domain. Moreover, antibody binding to the same two determinants was also inhibited when ZAP-70 or the SH2 domains bound to the zeta chain or to a 2pY-ITAM. Together, these two observations suggest a model in which intramolecular contacts keep ZAP-70 in a closed configuration with the two SH2 domains near to each other.

Amino Acid Sequence↗
PubMed1997

The MBP fusion protein restores the activity of the first phosphatase domain of CD45.

CD45 is a receptor-like protein tyrosine phosphatase critically involved in the regulation of initial effector functions in B- and T-cells. The protein comprises two phosphatase (PTP) domains in its cytoplasmic region. However, whether each PTP domain has enzyme activity by itself or whether both domains are required to build up a functional enzyme is unclear. We have studied different constructions of human CD45 comprising the two PTP domains, both separately and as a single protein, fused to maltose-binding protein (MBP). In apparent contrast with previous studies, we show that the first PTP domain of CD45 (when fused to MBP) may be a viable phosphatase in the absence of the second domain. Phosphatase activity resides in the monomeric form of the protein and is lost after proteolytic cleavage of the fusion partner, indicating that MBP specifically activates the first PTP domain. Furthermore, changes in the optimal pH for activity with respect to wild-type CD45 suggest that protein-protein interactions involving residues in the neighbourhood of the catalytic site mediate enzyme activation.

Binding Sites↗
PubMed1997

Two ldh genes from tomato and their expression in different organs, during fruit ripening and in response to stress.

Two different ldh genes have been isolated from a tomato genomic library and sequenced. Both contain a single intron and correspond to cDNA clones LeLdh1 and LeLdh2 isolated from a library constructed from hypoxically induced tomato roots. Southern blots indicate that the two genes comprise the entire ldh gene family in tomato. Both genes are expressed at low levels in leaves, fruit and roots. Their transcript levels do not change during fruit ripening. Ldh1 but not ldh2 is inducible by oxygen deficit in both roots and fruit.

Base Sequence↗
PubMed1997

Differential expression of two tomato lactate dehydrogenase genes in response to oxygen deficit.

Two different cDNAs encoding lactate dehydrogenase (LDH) were isolated from a library of hypoxically treated tomato roots and sequenced. The use of gene-specific probes on northern blots showed that Ldh2 mRNA was predominant in well-oxygenated roots and levels remained stable upon oxygen deficit; in contrast, Ldh1 mRNA accumulated to high levels within 2 h of hypoxia or anoxia. Immunoblot analyses of native gels using a polyclonal antiserum raised against an LDH1 fusion protein indicated that LDH2 homotetramer was the major isoform present in aerobic roots. Levels of both LDH1 and LDH2 subunits increased during an 18 h hypoxic treatment, together with a 5-fold rise in activity. These results suggest that the regulation of ldh1 expression is primarily at the transcriptional level while that of ldh2 is post-transcriptional. Increases in Ldh1 mRNA and LDH activity were not correlated with lactic acid production, which was maximal at the onset of anoxia in unacclimated roots and then declined. Taken together, our results indicate that LDH2 present in aerobic roots is principally responsible for lactic acid production occurring transiently upon imposition of anoxia. Possible physiological roles for LDH1 are discussed.

Amino Acid Sequence↗
PubMed1996

Mutation of tyrosines 492/493 in the kinase domain of ZAP-70 affects multiple T-cell receptor signaling pathways.

The protein-tyrosine kinase ZAP-70 is implicated, together with the Src kinase p56(lck), in controlling the early steps of the T-cell antigen receptor (TCR) signaling cascade. To help elucidate further the mechanism by which ZAP-70 regulates these initial events, we used a dominant-negative mutant approach. We overexpressed in the Jurkat T-cell line ZAP-70 mutated on Tyr-492 and Tyr-493 in the putative regulatory loop of its kinase domain. This mutant inhibited TCR-induced activation of nuclear factor of activated T cells by interfering with both intracellular calcium increase and Ras-regulated activation of extracellular signal-regulated kinases. Moreover, TCR-induced phosphorylation of pp36-38, thought to play a role upstream of these pathways, was found to be reduced. In contrast, overexpression of wild-type ZAP-70 induced constitutive activation of nuclear factor of activated T cells. The ZAP-70 mutant studied here could be phosphorylated on tyrosine when associated to the TCR zeta chain and was able to bind p56(lck). This result demonstrates that Tyr-492 and Tyr-493 are not responsible for the Src homology domain 2-mediated association of p56(lck) with ZAP-70. Our data are most consistent with a model in which recruitment to the TCR allows ZAP-70 autophosphorylation and binding to p56(lck), which in turn phosphorylates Tyr-492 and/or Tyr-493 with consequent up-regulation of the ZAP-70 kinase activity. ZAP-70 will then be able to effectively control phosphorylation of its substrates and lead to gene activation.

Adaptor Proteins, Signal Transducing↗
PubMed1996

The p56lck SH2 domain mediates recruitment of CD8/p56lck to the activated T cell receptor/CD3/zeta complex.

The CD4 or CD8 co-receptors and the T cell receptor (TCR) are though to interact with the same antigen-presenting major histocompatibility complex molecule in a stable ternary complex. Therefore, the TCR and its co-receptor need to come into close proximity on the surface of the T cell. We have previously shown that the interaction of the p56lck SH2 domain with zeta-associated, tyrosine phosphorylated ZAP-70 and Syk kinases leads to an enhanced association of CD4 with TCR/CD3/zeta complex after CD3 stimulation of Jurkat cells. In this report, we analyzed whether a similar mechanism can mediate recruitment of the CD8 alpha alpha and CD8 alpha beta isoforms to the TCR. We demonstrate in vivo in association of CD8 alpha alpha/p56lck with the tyrosine kinase ZAP-70 after CD3 stimulation of Jurkat cells. A phosphopeptide competing in vitro for the binding of tyrosine phosphorylated proteins to the SH2 domain of p56lck specifically impedes the association of ZAP-70 with CD8 alpha alpha/p56lck without affecting the zeta/ZAP-70 interaction. The same peptide is able to compete for the activation-dependent association of the CD8 alpha alpha or CD8 alpha beta isoform with the TCR/CD3/zeta complex. Moreover, co-precipitation of the TCR with both CD8 isoforms was observed after CD3 stimulation. These findings strongly suggest that the p56lck SH2 domain mediates recruitment of CD8/p56lck to the activated TCR/CD3/zeta complex.

Amino Acid Sequence↗
PubMed1986

Determinative factors in human tonotopy: tentative analysis.

Two main parameters of stimulation were checked as an attempt to investigate the limits of the tonotopic organization in the human auditory cortex. Auditory Evoked magnetic Field (AEF) experiments from a dozen normal subjects are reported. Five of them clearly showed tonotopic AEF responses to long tone bursts stimuli, which disappeared when equivalent white noise was superimposed to the tone. Discrepancies from previous reports and high inter-individual variability are discussed.

Adolescent↗
PubMed1980

[Value of high dosage propranolol and per-operative hypothermia in thyroidectomy when conventional preparatory treatment is unsuitable (author's transl)].

Five hyperthyroid patients could be prepared for surgery wit propranolol alone in daily doses of 240 to 400 mg. The drug administered for 3 to 5 days before, and 5 to 15 days after the operation. Following premedication with levopromazine, almost total thyroidectomy was performed under neuroleptanalgesia and moderate hypothermia. The immediate results were satisfactory and free from acute thyrotoxic crisis. On follow-up, 2 to 18 months after surgery 4 patients had clinically and biologically normal thyroid function, and one patient showed evidence of hypothyroidism. For the common forms of the disease the authors use the conventional preparatory treatment. However, they favour a short course of propranolol in high doses either when non-thyroid emergency operations require preliminary treatment of the patient's hyperthyroidism, or when the conventional treatment is ineffective or contra-indicated on account of haematological complications.

Adult↗
PubMedDate not supplied

[Effect of different variables on the outcome of various cognitive-behavioral treatment modalities for panic disorder with agoraphobia].

The efficacy of cognitive-behavioral therapy (CBT) is clearly demonstrated in the treatment of panic-disorder with agoraphobia (PDA). Between 70% and 90% of people with PDA obtain an higher global functioning level after CBT, yet symptoms remain in 10 to 30% of participants after treatment termination. The goal of the present study is to find which variables have an effect on different CBT modalities (individual, group, self-help) for persons with moderate and high PDA. Eighty-four persons were randomly assigned to one of three treatment modalities. Evaluations were made before treatment, immediately after and one year later. Results show that sex, number of years with agoraphobia and anxiety level significantly predict outcome at post-test for the individual modality. However, only the number of years with agoraphobia is a strong predictor one year later for this treatment modality. For the self-help modality, no predictor is significant neither at post-test nor one year later. For the group modality, the agoraphobic avoidance predicts outcome at post-test whereas symptoms severity predicts outcome one year later.

Adolescent↗