Electron fluctuation induced resonance broadening in nano electromechanical systems: the origin of shear force in vacuum.

This article presents a study of the poorly understood "shear-force" used in an important class of near-field instruments that use mechanical resonance feedback detection. In the case of a metallic probe near a metallic surface in vacuum, we show that in the 10-60 nm range there is no such a thing as a shear-force in the sense of the nonconservative friction force. Fluctuations of the oscillator resonance frequency, likely induced by local charge variations, could account for the reported effects in the literature without introducing a dissipative force.

[The N-terminal pro-brain natriuretic peptide (NT-proBNP) assay with the Stratus CS analyzer]. / Evaluation des performances analytiques du dosage du NT-proBNP sur analyseur semi-automatisé Stratus CS.

BACKGROUND: NT-proBNP is an efficient biomarker for the evaluation, management and prognosis of patients with heart failure. METHODS: We evaluated the analytical performance of the NT-proBNP immunoenzymatic assay with the Stratus CS semi-automated analyzer in two hospital laboratories. The characteristics assessed included imprecision, functional sensitivity, linearity/recovery, interferences study, high-dose hook effect and a comparison of Acute Care(TM) pPBNP (on Stratus)CS) versus PBNP (on Dimension HM) results on patient heparinized plasma samples. RESULTS: Total imprecision reached < 5% coefficient of variation at NT-proBNP concentrations of 186-19,649 ng/L; recovery values for diluted samples were between 89.0 and 110.0 %; functional sensitivity reached 21 ng/L; there was no high-dose hook effect at concentrations up to 400,000 ng/L; hemaoglobin affected negatively but <10% the NT-proBNP assay, while bilirubin and triglycerides did not affected it more than 5%; Stratus CS results were strongly correlated with Dimension HM results (R(2)=1,00). CONCLUSION: The Stratus CS Acute Care pPBNP assay demonstrated excellent analytical performance which agreed with the Dimension HM PBNP assay. This analyzer is therefore suitable for use by low NT-proBNP test volume laboratories, and also by Emergency departments and Intensive care units.

Effect of mutagen-induced cell lethality on the dose response of germline mutations.

Molecular tests for mutations require a sample of tissue from which DNA is extracted, to determine the presence or absence of one or more mutations per sample. To ensure mutation fixation each sample must consist of an equal number of cells that have had one or more DNA replications. In an in vivo test, surviving stem cells compensate to give the same number of cells per sample, leaving as the only evidence for stem cell lethality the increase in mutants of clonal origin because the mutant clone developed from a population of fewer stem cells. A problem is that an increase in mutagen dose increases stem cell death, resulting in a decreased number of surviving target cells, thus giving a downward bias of samples with one or more mutations per sample. To compare in vivo tests with molecular tests we will use as a model system the sex-linked recessive lethal (SLRL) test for germ cell mutations in Drosophila melanogaster. Spermatogonia cells in male larvae were exposed to ENU and mutations detected in sperm cells from adults. The same SLRL data were analyzed by two methods: (1) The conventional analysis of SLRL data, in which each mutation of a cluster of mutations of common origin was counted. (2) An analysis was used to simulate a sample for molecular analysis by determining mutations per male with an equal size sample of progeny per male. With this second analysis a correction factor is required based on the change in cluster size of mutants of common origin.

A specific role for the phosphorylation of mammalian acidic ribosomal protein P2.

The acidic ribosomal proteins P1-P2 from rat liver were overproduced for the first time by expression of their cDNA in Escherichia coli. They were tested for their ability to reactivate inactive P1-P2-deficient core particles derived from 60 S ribosomal subunits treated with dimethylmaleic anhydride, in poly(U)-directed poly(Phe) synthesis. The recombinant P1-P2 were unable to reactivate these core particles although they could bind to them. When recombinant P1-P2 had been phosphorylated first with casein kinase II, they were as efficient in the reactivation process as P1-P2 extracted with ethanol/KCl from the 60 S subunits. Reconstitution experiments were carried out using all possible combinations of the two recombinant proteins phosphorylated or not. Reactivation of the core particles required the presence of both P1 and P2 with the latter in its phosphorylated form. These experiments reveal a distinct role for P1 and P2 in protein synthesis. Phosphorylated P2 produced a partial quenching of the intrinsic fluorescence of eukaryotic elongation factor 2, which was not observed with the unphosphorylated protein. This result demonstrates the existence of an interaction between phosphorylated P2 and eukaryotic elongation factor 2. P2 also quenched part of the intrinsic fluorescence of P1, due to the interaction between the two proteins.

Photoaffinity labeling of elongation factor-2 with 8-azido derivatives of GTP and ATP.

Elongation factor 2 (eEF-2) can interact not only with guanylic nucleotides but also with adenylic ones, as was shown by intrinsic fluorescence quenching studies [Sontag, B., Reboud, A.M., Divita, G., Di Pietro, A., Guillot, D. & Reboud, J.P. (1993) Biochemistry 32, 1976-1980]. Here we studied sites of these interactions by using photoactivable 8-azido-[gamma-32P]GTP and 8-azido-[gamma-32P]ATP. Photoincorporation of the radioactive GTP derivative into eEF-2 was prevented by the previous addition of GTP and GDP. The addition of adenylic nucleotides (ATP, ADP) and some adenylic derivatives [NAD+, NADH,poly(A)] decreased the photoincorporation by only 40% at most. However, photoincorporation of the radioactive ATP derivative was prevented by the previous addition not only of adenylic compounds [ATP, ADP, NAD+, NADH, poly(A)] but also of GTP and GDP. Photoincorporation of radioactive nucleotide derivatives was not decreased by the addition of other nucleotidic compounds [UTP, poly(U), ITP, NADP+, NADPH]. ATP and GTP acted as non-competitive inhibitors of the photoincorporation of 8-azido-[gamma-32P]GTP and 8-azido-[gamma-32P]ATP, respectively. eEF-2 photolabeled with these radioactive nucleotide derivatives was submitted to trypsin digestion under different conditions and the labeled peptidic fragments identified after HPLC purification and gel electrophoresis by N-terminal sequencing. An octapeptide, Y264FDPANGK271, was the only peptide photolabeled with 8-azido-[gamma-32P]GTP whereas a N-terminal fragment of about 7 kDa was the only one photolabeled with 8-azido-[gamma-32P]ATP. The different results support the hypothesis that guanylic and adenylic nucleotides do not interact with the same site of eEF-2.

Interaction of phosphorylated elongation factor EF-2 with nucleotides and ribosomes.

The intrinsic fluorescence emission spectrum of elongation factor EF-2 due to the 7 Trp residues was not modified after complete phosphorylation of the factor by the specific Ca2+/Calmodulin-dependent kinase III. The effect of nucleotide binding on this fluorescence revealed differences between phosphorylated and unmodified EF-2. Low concentrations of GTP had a smaller quenching effect on the fluorescence of phosphorylated EF-2 than on the fluorescence of unmodified EF-2, whereas GDP had exactly the same quenching effect on the fluorescence of both samples. These results suggest that phosphorylation of EF-2 decreased its affinity for GTP but not for GDP. Ability of phosphorylated EF-2 to form a ternary complex with ribosomes in the presence of a non-hydrolysable GTP analog and its ability to protect ribosomes against ricin-inactivation were both decreased to the same extent. The lower affinity of phosphorylated EF-2 for GTP could be responsible for a weaker and/or incorrect interaction of the factor with the ribosome, in particular with the ricin-site of the 28-S rRNA assumed to be involved in translocation initiation.

[Spontaneous intramural hematoma of the esophagus. Apropos of a case]. / Hématome spontané intramural de l'oesophage. A propos d'un cas.

The authors report a case of spontaneous intramural haematoma of the oesophagus. This is a rare observation which usually occurs in association with oesophageal hyperpressure and sometimes with impaired haemostasis. The strategy for diagnosis is based on tomodensitography and also endosonography and magnetic resonance imagery.

[Ischemic cerebral vascular accidents in young subjects and livedo reticularis. Apropos of a case of Sneddon's syndrome or Divry-Van Bogaert's syndrome]. / Accidents vasculaires cérébraux ischémiques du sujet jeune et livedo réticulaire. A propos d'un cas de syndrome de Sneddon ou de Divry-Van Bogaert.

The authors report the case of a 28-year-old patient presenting with successive ischaemic cerebral vascular accidents, preceded by the appearance of a livedo reticulare, without any laboratory signs of an inflammatory syndrome. Since Sneddon, and before him Divry and Von Bogaert, patients with this dermatosis are known to have an increased frequency of ischaemic cerebral vascular accidents. This syndrome, considered for a long time to be minimally aggressive, appears to be a very serious disease, leading to a bedridden state and dementia. The prognosis for these patients, all young (30-40 years), therefore appears to be very poor. Any case of livedo reticulare requires the search for cerebral neurological lesions. After a complete neurological examination, imaging therefore has an important major in the assessment of cerebral lesions due to this corticomeningeal angiomatosis. CT scan and MRI are useful in this initial assessment and in the subsequent follow-up of patients. In cases with frank neurological lesions, cerebral arterial exploration is essential with demonstration of lesions of the midcerebral arteries and activation of collateral vascular anastomoses and their helicine vessels. The prognosis is based on the extent of these lesions. Cerebral biopsy may demonstrate a non-inflammatory endothelial cellular proliferation of midcerebral vessels.

Trp221 is involved in the protective effect of elongation factor eEF-2 on the ricin/alpha-sarcin site of the ribosome.

Elongation factor eEF-2 treated by N-bromosuccinimide under conditions which oxidize 2 Trp residues (Trp343 and Trp221) is inactivated in ribosome-dependent GTP hydrolysis and polyphenylalanine synthesis, and inactivation correlates with the specific oxidation of Trp221 (Guillot, D., Penin, F., Di Pietro, A., Sontag, B., Lavergne, J. P., and Reboud, J. P. (1993) J. Biol. Chem. 268, 20911-20916). It is shown here that this oxidation prevents neither GTP binding to eEF-2 nor the formation of the ribosome-eEF-2-GPP(NH)P complex, but that oxidized eEF-2 is no longer able to protect ribosomes against ricin inactivation. These observations suggest that Trp221 or an amino-acid sequence containing this residue interacts with the 28 S rRNA loop including the GAGA sequence, which is the target of ricin. Such a hypothesis is discussed in relation with data on RNA recognition motifs described in different proteins.

GTP binding to elongation factor eEF-2 unmasks a tryptophan residue required for biological activity.

Elongation factor eEF-2 from rat liver, which contains 7 tryptophan residues, was treated with increasing concentrations of N-bromosuccinimide (NBS) under conditions in which these residues were oxidized specifically. The reagent produced a characteristic lowering in both the absorbance at 280 nm and the intrinsic fluorescence at 332 nm of the factor. Fluorometric titration of tryptophans and correlation to eEF-2 residual activity on GTP hydrolysis and polyphenylalanine synthesis showed that modification of the two most reactive tryptophans completely inactivated the factor. These residues were identified as Trp343 and Trp221 after cleavage of the protein with cyanogen bromide, separation of the fragments by reversed-phase high-pressure liquid chromatography, and N-terminal sequencing of the two fragments which exhibited a decreased absorbance in the NBS-treated protein. Oxidation of the most reactive residue, Trp343, did not induce significant decrease of activity of the factor or of its ability to interact with GTP or GDP. On the contrary, oxidation of Trp221 inactivated the factor, whose residual fluorescence was still partly quenched by GDP but no longer by GTP. Preincubation of eEF-2 with GDP protected Trp221 against NBS oxidation and prevented concomitant inactivation of the factor, whereas preincubation of eEF-2 with GTP increased the sensitivity of the same Trp221 residue to the reagent. Our results show for the first time that Trp221, which is conserved and belongs to a well preserved domain in eukaryotic cells and archaebacteria, plays an essential part in the catalytic activity of eEF-2. They strongly suggest that GTP induces a conformational change of the protein which unmasks this residue, whereas GDP stabilizes a conformation which makes this residue much less accessible.

[Unusual radiologic aspect of a hydatid cyst]. / Aspect radiologique inhabituel d'un kyste hydatique.

The authors report us about an unusual hydatid cyst of the liver. Ultrasound, CT and MRI exams were used, and showed an unusual fatty component inside the lesion. The development of the disease in steatosic liver is not enough to explain the unusual density.

Intrinsic tryptophan fluorescence of rat liver elongation factor eEF-2 to monitor the interaction with guanylic and adenylic nucleotides and related conformational changes.

Elongation factor 2 (eEF-2), which contains seven Trp residues, exhibited a tryptophan-characteristic intrinsic fluorescence with maximum excitation at 280 nm and an emission peak centered at 333 nm that suggested a hydrophobic environment of these tryptophans. Upon denaturation with 6 M guanidine hydrochloride, the maximum emission was shifted to 348 nm. Fluorescence quenching studies using acrylamide and iodide confirmed that the Trp residues were mainly buried in the native molecule and indicated an important heterogeneity, the fractional accessible fluorescence (fa) values being 0.50 and 0.25, respectively. Partial quenching of eEF-2 fluorescence by nucleotides proved the existence of an interaction of the factor in the absence of ribosomes, not only with GDP but also with GTP, nonhydrolyzable analogs, GMP, and adenylic, but not cytidylic, nucleotides. Saturating binding plots showed different maximal changes of fluorescence depending upon the nucleotides, from 6.4% with ADP to 24.5% with GDP, and suggested the existence of more than one binding site for each nucleotide. Among all the nucleotides tested, only GTP at saturating concentration modified the fa value obtained with acrylamide (-36%). The possibility that this modification is related to a conformational change of eEF-2 induced by GTP binding is discussed.

[Marchiafava-Bignami's disease with a favourable course. Apropos of a case]. / Maladie de Marchiafava-Bignami d'évolution favorable. A propos d'un cas.

A resolving form of Marchiafava-Bignami disease is reported. This patient with a history of chronic alcoholism was hospitalised for a recent demential syndrome. Clinical examination did not show any signs of interhemispheric disconnection LP and EEG were normal. CT examination showed a low density area in the corpus callosum without any other anomaly. MRI examination confirmed the cystic area of the corpus callosum. The Marchiafava-Bignami disease was easily suggested on the basis imaging and clinical signs. Interhemispheric disconnection is not always found so MRI and CT examinations seem to be very useful tools for early diagnosis of Marchiafava-Bignami in the same way as neuropsychological tests.

Binding of GDP to a ribosomal protein after elongation factor-2 dependent GTP hydrolysis.

Incubation of 80S ribosomes with a substoichiometric amount of [alpha-32P]GTP and with eEF-2 resulted in the specific labeling of one ribosomal protein which migrated very close to the position of the acidic phosphoprotein P2 from the 60S subunit in two-dimensional isofocusing-SDS gel electrophoresis. Localization of protein P2 in this electrophoretic system was ascertained by correlation with its position in the standard two-dimensional acidic-SDS gel electrophoresis after its specific phosphorylation by casein kinase II. Labeling of the ribosomal protein was dependent on the presence of eEF-2, and could be attributed to [alpha-32P]GDP binding from the results of chase experiments and HPLC identification, this binding being very likely responsible for the slight shift in the electrophoretical position of the protein. Incubation of ribosomes with tRNA(Phe) in the absence of mRNA induced the release of the bound GDP.

[Post-traumatic osteolysis of the distal end of the clavicle. Contribution of MRI]. / Ostéolyse post-traumatique de l'extrémité distale de la clavicule. Apport de L'RM.

The authors describe a case of post-traumatic osteolysis of the clavicle. The clinical and roentgenographic aspects are well known. But regarding the lytic X ray aspect, another diagnosis, particularly a tumor may be evoked. Scintigraphy and computed tomograms can take a part in the diagnosis. But scanograms are uneasy to do in this region. The MRI allows to delimit the lesion, and the hypointense signal in T1 and T2 weighted sequences directs to a fibrosis in the area between the end of the clavicle and the acromion. In this case report, the relation between the MRI findings and the pathological aspects was good.

Alargamiento de los miembros superiores / Lenghtening of upper extremities

Se presentan dos pacientes con discrepancia en la longitud de los miembros superiores, cuya causa fue una osteomielitis de la metáfisis proximal del húmero en un paciente y una lesión de la placa epifisaria por ablación de una tumoración a ese nivel en el otro. Fue utilizada la técnica de Ilizarov por compactectomía, previa colocación del fijador externo, seguido posteriormente por la distracción gradual y progresiva a razón de 0,25 mm cada 6 horas, y se logra en ambos pacientes corregir el acortamiento que era de 9 cm en un paciente y de 11 cm en el otro. La complicación encontrada en los dos casos fue una parálisis radial, de la cual se recuperaron totalmente los pacientes al retirar el fijador externo. El objetivo de alargar un miembro superior corto es de índole estética y sicológica. El resultado final fue excelente (AU)