Markedly increased risk of postoperative bleeding complications during perioperative bridging anticoagulation in general and visceral surgery

BACKGROUND

Increasing numbers of patients receiving oral anticoagulants are undergoing elective surgery. Low molecular weight heparin (LMWH) is frequently applied as bridging therapy during perioperative interruption of anticoagulation. The aim of this study was to explore the postoperative bleeding risk of patients receiving surgery under bridging anticoagulation.

METHODS

We performed a monocentric retrospective two-arm matched cohort study. Patients that received perioperative bridging anticoagulation were compared to a matched control group with identical surgical procedure, age, and sex. Emergency and vascular operations were excluded. The primary endpoint was the incidence of major postoperative bleeding. Secondary endpoints were minor postoperative bleeding, thromboembolic events, length of stay, and in-hospital mortality. Multivariate analysis explored risk factors of major postoperative bleeding.

RESULTS

A total of 263 patients in each study arm were analyzed. The patient cohort included the entire field of general and visceral surgery including a large proportion of major oncological resections. Bridging anticoagulation increased the postoperative incidence of major bleeding events (8% vs. 1%; p < 0.001) as well as minor bleeding events (14% vs. 5%; p < 0.001). Thromboembolic events were equally rare in both groups (1% vs. 2%; p = 0.45). No effect on mortality was observed (1.5% vs. 1.9%). Independent risk factors of major postoperative bleeding were full-therapeutic dose of LMWH, renal insufficiency, and the procedure-specific bleeding risk.

CONCLUSION

Perioperative bridging anticoagulation, especially full-therapeutic dose LMWH, markedly increases the risk of postoperative bleeding complications in general and visceral surgery. Surgeons should carefully consider the practice of routine bridging.

Indication for allogeneic stem cell transplantation in Glanzmann’s thrombasthenia

Glanzmann’s thrombasthenia (GT) is an autosomal recessive disorder characterized by a lack of thrombocyte aggregation due to the absence of thrombocyte glycoproteins IIb and αIIbβ3. The role of haematopoietic stem cell transplantation (HSCT) in GT remains controversial. However, HSCT offers the only curative approach for patients with a severe clinical phenotype.

In this review, we will discuss the limitation of current status evidence and the specific risk of GT, in particular the alloimmunization and refractoriness to thrombocyte infusions. 19 successful HSCT in 18 GT type I patients have been reported. Mean age at transplantation was 5 years. All patients are still alive. The majority received sibling bone marrow transplant with busulfan and cyclophosphamid conditioning. GvHD incidence was within the normal range, but 10 patients showed alloimmunization of thrombocytes. Median follow up is 25 months.

[Distal Forearm Fractures in Children and Adolescents: Frequency and Health Care Provision in Germany]

BACKGROUND

Despite their frequent occurrence, there are no standardized recommendations for treating distal forearm fractures in growing children. Due to the marked remodelling capacity, conservative therapy is the first choice treatment of fractures in children. However, there are concerns that the possibilities of conservative treatments are often underestimated. Information on the health care situation in Germany on this issue is scarce.

METHODS

The present study is based on routine data of a German Health Insurance fund, the Gmünder ErsatzKasse (GEK). Data on diagnoses and treatment of insured persons aged 0-15 years were analysed for the period from 01/07/2005 to 30/06/2009 regarding the frequency of distal forearm fractures and fracture treatment.

RESULTS

The overall incidence rate was 56.8 per 10 000 person-years (64.5 in boys; 48.7 in girls). Most of the distal forearm fractures occurred during spring and summer months. The majority of the fractures were immobilized in a plaster cast (84.2%; n=2 609). 8.7% (n=270) of the fractures were treated with closed reduction and percutaneous osteosynthesis. 4.5% (n=138) were treated with closed reduction without any form of osteosynthesis. Only 1.4% (n=43) of the fractures were treated with open reduction.

CONCLUSION

Our study shows that boys suffer distal forearm fractures more frequently than girls and that incidences tend to be higher in older children. In addition, analyses indicated seasonal differences between the age groups. In childhood, distal forearm fractures were treated more often conservatively than operatively. However, it was remarkable that fractures in the case of closed reduction were more frequently fixed with an osteosynthesis than just by immobilization in a plaster cast.

A magnetohydrodynamic model of solar wind interaction with asteroid gaspra

The solar wind response to a small-sized magnetized body is modeled on the basis of a two-dimensional magnetohydrodynamic (MHD) plasma description including Hall current corrections (Hall-MHD model). Basic features of the magnetic signatures observed near Galileo's closest approach to asteroid Gaspra are reproduced, assuming Gaspra's magnetic dipole momentto be of the order of 10(14) ampere.meters squared and tilted to the solar wind flow direction at an angle of about 45 degrees .

Procedure for rapid isolation of photosynthetic reaction centers using cytochrome c affinity chromatography

Horse heart cytochrome c linked to Sepharose 4B is used to purify reaction centers from Rhodopseudomonas sphaeroides R-26. This procedure allows for an initial recovery of 80-90% of the bacterial reaction centers present in chromatophore membranes. High purity reaction centers (A(280)/A(802) < 1.30) can be obtained with a 30% recovery. Reaction centers from wild-type Rps. sphaeroides and Rps. capsulata also bind to a cytochrome c column. Cytochrome c affinity chromatography can also be used to isolate photosystem I complexes from spinach chloroplasts.

Labeling quinone-binding sites in photosynthetic reaction centers: A 38-kilodalton protein associated with the acceptor side of photosystem II

2-Acetoxymethyl-1,4-naphthoquinone (2-AcOMeNQ) binds with rapid kinetics and high affinity to the primary quinone Q(A) site of reaction centers from Rhodopseudomonas capsulata. Binding of 2-AcOMeNQ fully restores electron-transfer activity with kinetics that is similar, but not identical, to that seen with ubiquinone-50. When bound at the Q(A) site, 2-AcOMeNQ preferentially labels the L subunit. This preference suggests that 2-AcOMeNQ labels primarily the region of a quinone-binding site that is close to the first isoprenoid unit of the side chain, which is expected from the location and structure of the reaction region of the molecule. In photosystem II particles from Synechococcus sp., 2-AcOMeNQ primarily labels two polypeptides with apparent molecular masses of 38 and 19 kDa. Labeling of only the 38-kDa polypeptide is sufficiently sensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) to conclude that it is involved in binding quinones on the acceptor side of photosystem II. Although we have not yet identified the 38-kDa protein, its properties suggest that it is the D2 protein. From the DCMU-sensitive labeling and from homologies to functionally important regions of the bacterial reaction-center subunits, we propose that the 38-kDa protein is intimately involved in binding the cofactors that mediate primary photochemistry.

Photooxidation of antenna bacteriochlorophyll in chromatophores from carotenoidless mutant Rhodopseudomonas sphaeroides and the attendant loss of dimeric exciton interaction

Intense continuous illumination of purified chromatophores from carotenoidless mutant Rhodopseudomonas sphaeroides results in progressive photooxidative loss of the near infrared absorption band near 860 nm assigned to antenna bacteriochlorophyll. The quantum yield of this reaction is low, approximately 1.7 x 10(-5). The loss in near infrared absorption is accompanied by a proportional shift in the absorption maximum to shorter wavelengths. The double circular dichroism feature in the near infrared decreases at a faster rate than does the absorbance. These results are explained by a model in which the antenna bacteriochlorophyll, initially associated as dimers (lambda(max) = 860.2 nm), is progressively converted to the monomeric state (lambda(max) = 851.9 nm). The wavelength shift is attributed to disruption of exciton coupling in the dimer. Acetone/methanol extraction indicates that the maximum molar extinction coefficients of the dimer and monomer do not differ by more than 4%. The occurrence of an absorption maximum at 852 nm for monomeric bacteriochlorophyll in a protein complex demonstrates that it is not necessary to invoke aggregation of the chromophores as the origin of the shift from 770 nm in typical organic solvents.

Montelukast does not prevent reactive airway disease in young children hospitalized for RSV bronchiolitis

AIM

To evaluate the long-term effect of montelukast on symptoms of cough and wheeze following RSV bronchiolitis.

METHODS

Fifty eight patients (aged < or = 24 months) hospitalized with a first episode of RSV bronchiolitis were enrolled in this double blind prospective randomized trial comparing montelukast (n = 31) vs placebo (n = 27).

RESULTS

During the 3-month treatment period, there were no statistical significant differences between the two groups for symptom-free days and nights (48.5 [interquartile range 33.0.0-66.0] for montelukast vs 57.0 [29.0-71.0] for placebo p = 0.415) nor disease-free days and nights (44.5 days [26.0-54.0] vs 53.0 [22.3-71.0]; p = 0.266). During the 1 year follow-up, there were 41 exacerbations in the montelukast group vs 54 exacerbations in the placebo group (p = 0.57). Time to first exacerbation was not different. Number of unscheduled visits and need to start inhaled steroids were comparable in the two groups.

CONCLUSION

Treatment with montelukast after hospital admission for RSV bronchiolitis in children younger than 2 years of age did not reduce symptoms of cough and wheeze. We cannot exclude that a subgroup of children may, however, benefit from this treatment.

Molecular Orientation in Quantasomes: III. A Flow Dichroism Apparatus and Its Application to the Study of the Structure of Spinach Quantasomes

A new apparatus is described for measuring dichroism spectra with very high sensitivity for macromolecular structures oriented in a hydrodynamic gradient. The method has been used to explore the dichroism spectrum of quantasome aggregates isolated from spinach chloroplasts. The quantasome flow dichroism resembles qualitatively that observed previously using electric field orientation, in that a pigment absorbing at wavelengths longer than 680 mmu exhibits appreciably greater dichroism than those absorbing at shorter wavelengths. It is shown that the absorption oscillator for this long wavelength absorption lies parallel to the streamlines of the sheer gradient, which is assumed to be the direction in which the planes of the chloroplast lamellae are oriented.

Palliative Sedierung

Terminal illnesses can cause distressing symptoms such as severe pain, mental confusions, feelings of suffocation, and agitation. Despite skilled palliative care in some cases these symptoms may not respond to standard interventions. After all other means to provide comfort and relief to a dying patient have been tried and are unsuccessful, clinical caregivers and patients can consider palliative sedation. Sedation in the context of palliative medicine is the monitored use of medications to induce varying degrees of unconsciousness to bring about a state of decreased or absent awareness in order to relieve the burden of otherwise refractory suffering. Palliative sedation is not intended to cause death or shorten life. The patient and family should agree with plans for palliative sedation. Because cases involving palliative sedation are emotionally stressful, the patient, family, and health care workers can all benefit from talking about the complex medical, ethical, and emotional issues they raise.

Calcium influences cellular and extracellular product formation during biofilm-associated growth of a marine Pseudoalteromonas sp

Bacteria undergo a variety of physiological changes following a switch from planktonic growth to surface-associated biofilm growth. Here, it is shown that biofilm development of a marine isolate, Pseudoalteromonas sp. 1398, results in global changes in its cytosolic and extracellular proteomes. Calcium influences these proteome responses, and affects the amount of surface-associated biomass and extracellular matrix material produced by Pseudoalteromonas sp. 1398. Four extracellular proteins, characterized by N-terminal sequencing, showed increased abundances, while one protein, flagellin, showed reduced abundance at higher [Ca2+]. Immunoblotting and transmission-electron-microscopy analysis confirmed that higher [Ca2+] and surface-associated growth results in the repression of flagella production. Two-dimensional gel electrophoresis (2DGE) studies combined with cluster analysis of global proteome responses demonstrated that Ca2+ had a greater regulatory influence on Pseudoalteromonas sp. growing in biofilms than on planktonic cultures. Approximately 22 % of the total cytosolic proteins resolved by 2DGE had differing abundances in response to a switch from planktonic growth to surface-associated growth when the cells were cultivated in 1 mM Ca2+. At higher [Ca2+] this number increased to 38 %. Fifteen cellular proteins that were differentially expressed in response to biofilm growth and/or Ca2+ were analysed by N-terminal sequencing and/or MS/MS. These proteins were identified as factors involved in cellular metabolic functions, putative proteases and transport proteins, although there were several proteins that had not been previously characterized. These results indicate that Ca2+ causes global changes in matrix material, as well as in cellular and extracellular protein profiles of Pseudoalteromonas sp. 1398. These changes are more pronounced when the bacterium grows in biofilms than when it grows in planktonic culture.

Direct reconstruction of kinetic parameter images from dynamic PET data

Our goal in this paper is the estimation of kinetic model parameters for each voxel corresponding to a dense three-dimensional (3-D) positron emission tomography (PET) image. Typically, the activity images are first reconstructed from PET sinogram frames at each measurement time, and then the kinetic parameters are estimated by fitting a model to the reconstructed time-activity response of each voxel. However, this "indirect" approach to kinetic parameter estimation tends to reduce signal-to-noise ratio (SNR) because of the requirement that the sinogram data be divided into individual time frames. In 1985, Carson and Lange proposed, but did not implement, a method based on the expectation-maximization (EM) algorithm for direct parametric reconstruction. The approach is "direct" because it estimates the optimal kinetic parameters directly from the sinogram data, without an intermediate reconstruction step. However, direct voxel-wise parametric reconstruction remained a challenge due to the unsolved complexities of inversion and spatial regularization. In this paper, we demonstrate and evaluate a new and efficient method for direct voxel-wise reconstruction of kinetic parameter images using all frames of the PET data. The direct parametric image reconstruction is formulated in a Bayesian framework, and uses the parametric iterative coordinate descent (PICD) algorithm to solve the resulting optimization problem. The PICD algorithm is computationally efficient and is implemented with spatial regularization in the domain of the physiologically relevant parameters. Our experimental simulations of a rat head imaged in a working small animal scanner indicate that direct parametric reconstruction can substantially reduce root-mean-squared error (RMSE) in the estimation of kinetic parameters, as compared to indirect methods, without appreciably increasing computation.

Characterization of nutrient-induced dispersion in Pseudomonas aeruginosa PAO1 biofilm

The processes associated with early events in biofilm formation have become a major research focus over the past several years. Events associated with dispersion of cells from late stage biofilms have, however, received little attention. We demonstrate here that dispersal of Pseudomonas aeruginosa PAO1 from biofilms is inducible by a sudden increase in carbon substrate availability. Most efficient at inducing dispersal were sudden increases in availability of succinate > glutamate > glucose that led to approximately 80% reductions in surface-associated biofilm biomass. Nutrient-induced biofilm dispersion was associated with increased expression of flagella (fliC) and correspondingly decreased expression of pilus (pilA) genes in dispersed cells. Changes in gene expression associated with dispersion of P. aeruginosa biofilms were studied by using DNA microarray technology. Results corroborated proteomic data that showed gene expression to be markedly different between biofilms and newly dispersed cells. Gene families that were upregulated in dispersed cells included those for flagellar and ribosomal proteins, kinases, and phage PF1. Within the biofilm, genes encoding a number of denitrification pathways and pilus biosynthesis were also upregulated. Interestingly, nutrient-induced dispersion was associated with an increase in the number of Ser/Thr-phosphorylated proteins within the newly dispersed cells, and inhibition of dephosphorylation reduced the extent of nutrient-induced dispersion. This study is the first to demonstrate that dispersal of P. aeruginosa from biofilms can be induced by the addition of simple carbon sources. This study is also the first to demonstrate that dispersal of P. aeruginosa correlates with a specific dispersal phenotype.

Biofilms as complex differentiated communities

Prokaryotic biofilms that predominate in a diverse range of ecosystems are often composed of highly structured multispecies communities. Within these communities metabolic activities are integrated, and developmental sequences, not unlike those of multicellular organisms, can be detected. These structural adaptations and interrelationships are made possible by the expression of sets of genes that result in phenotypes that differ profoundly from those of planktonically grown cells of the same species. Molecular and microscopic evidence suggest the existence of a succession of de facto biofilm phenotypes. We submit that complex cell-cell interactions within prokaryotic communities are an ancient characteristic, the development of which was facilitated by the localization of cells at surfaces. In addition to spatial localization, surfaces may have provided the protective niche in which attached cells could create a localized homeostatic environment. In a holistic sense both biofilm and planktonic phenotypes may be viewed as integrated components of prokaryote life.

Regulation of the embryonic cell proliferation by Drosophila cyclin D and cyclin E complexes

Cell proliferation during Drosophila development occurs in a well known spatial and temporal pattern which can readily be studied in vivo. The cells which form the larval epidermis exit from the cell division cycle during embryogenesis after the 16th round of mitosis when they enter for the first time into a G1/0 phase. We are interested in the mechanistic basis of this cell proliferation arrest. We have shown that the arrest requires the down-regulation of cyclin E/Cdk2 activity by inhibition of cyclin E expression and parallel activation of Dacapo/p27 expression. In addition, up-regulation of Fizzy-related is observed and is required for inhibition of Cdk1 activity. Do these processes result from the down-regulation of D-type cyclin/Cdk complexes? Extensive evidence from mammalian cells, and in particular from tumour cells has suggested that these complexes act as master regulators of cell proliferation upstream of cyclin E. Our genetic analyses indicate that Drosophila cyclin D/Cdk4, which interacts with the Drosophila Rb family member as expected, does not play an essential role in the regulation of cell proliferation.

Hematopoietic progenitor kinase 1 associates physically and functionally with the adaptor proteins B cell linker protein and SLP-76 in lymphocytes

B cell linker protein (BLNK) is a SLP-76-related adaptor protein essential for signal transduction from the BCR. To identify components of BLNK-associated signaling pathways, we performed a phosphorylation-dependent yeast two-hybrid analysis using BLNK probes. Here we report that the serine/threonine kinase hematopoietic progenitor kinase 1 (HPK1), which is activated upon antigen-receptor stimulation and which has been implicated in the regulation of MAP kinase pathways, interacts physically and functionally with BLNK in B cells and with SLP-76 in T cells. This interaction requires Tyr(379) of HPK1 and the Src homology 2 (SH2) domain of BLNK/SLP-76. Via homology modeling, we defined a consensus binding site within ligands for SLP family SH2 domains. We further demonstrate that the SH2 domain of SLP-76 participates in the regulation of AP-1 and NFAT activation in response to T cell receptor (TCR) stimulation and that HPK1 inhibits AP-1 activation in a manner partially dependent on its interaction with SLP-76. Our data are consistent with a model in which full activation of HPK1 requires its own phosphorylation on tyrosine and subsequent interaction with adaptors of the SLP family, providing a mechanistic basis for the integration of this kinase into antigen receptor signaling cascades.

Characterization of phenotypic changes in Pseudomonas putida in response to surface-associated growth

The formation of complex bacterial communities known as biofilms begins with the interaction of planktonic cells with a surface. A switch between planktonic and sessile growth is believed to result in a phenotypic change in bacteria. In this study, a global analysis of physiological changes of the plant saprophyte Pseudomonas putida following 6 h of attachment to a silicone surface was carried out by analysis of protein profiles and by mRNA expression patterns. Two-dimensional (2-D) gel electrophoresis revealed 15 proteins that were up-regulated following bacterial adhesion and 30 proteins that were down-regulated. N-terminal sequence analyses of 11 of the down-regulated proteins identified a protein with homology to the ABC transporter, PotF; an outer membrane lipoprotein, NlpD; and five proteins that were homologous to proteins involved in amino acid metabolism. cDNA subtractive hybridization revealed 40 genes that were differentially expressed following initial attachment of P. putida. Twenty-eight of these genes had known homologs. As with the 2-D gel analysis, NlpD and genes involved in amino acid metabolism were identified by subtractive hybridization and found to be down-regulated following surface-associated growth. The gene for PotB was up-regulated, suggesting differential expression of ABC transporters following attachment to this surface. Other genes that showed differential regulation were structural components of flagella and type IV pili, as well as genes involved in polysaccharide biosynthesis. Immunoblot analysis of PilA and FliC confirmed the presence of flagella in planktonic cultures but not in 12- or 24-h biofilms. In contrast, PilA was observed in 12-h biofilms but not in planktonic culture. Recent evidence suggests that quorum sensing by bacterial homoserine lactones (HSLs) may play a regulatory role in biofilm development. To determine if similar protein profiles occurred during quorum sensing and during early biofilm formation, HSLs extracted from P. putida and pure C(12)-HSL were added to 6-h planktonic cultures of P. putida, and cell extracts were analyzed by 2-D gel profiles. Differential expression of 16 proteins was observed following addition of HSLs. One protein, PotF, was found to be down-regulated by both surface-associated growth and by HSL addition. The other 15 proteins did not correspond to proteins differentially expressed by surface-associated growth. The results presented here demonstrate that P. putida undergoes a global change in gene expression following initial attachment to a surface. Quorum sensing may play a role in the initial attachment process, but other sensory processes must also be involved in these phenotypic changes.

Attenuated total reflection design for in situ FT-IR spectroelectrochemical studies

A versatile spectroelectrochemical apparatus is introduced to study the changes in IR spectra of organic and inorganic compounds upon oxidation or reduction. The design is based on an attenuated total reflection device, which permits the study of a wide spectral range of 16,700 (600 nm)-250 cm(-1), with a small opaque region of 2250-1900 cm(-1). In addition, an IR data collection protocol is introduced to deal with electrochemically nonreversible background signals. This method is tested with ferrocene in acetonitrile; concentrations as low as 1 mM produce results that agree with those in the literature.

Absence of Mn-centered oxidation in the S(2) --> S(3) transition: implications for the mechanism of photosynthetic water oxidation

A key question for the understanding of photosynthetic water oxidation is whether the four oxidizing equivalents necessary to oxidize water to dioxygen are accumulated on the four Mn ions of the oxygen-evolving complex (OEC), or whether some ligand-centered oxidations take place before the formation and release of dioxygen during the S(3) --> [S(4)] --> S(0) transition. Progress in instrumentation and flash sample preparation allowed us to apply Mn Kbeta X-ray emission spectroscopy (Kbeta XES) to this problem for the first time. The Kbeta XES results, in combination with Mn X-ray absorption near-edge structure (XANES) and electron paramagnetic resonance (EPR) data obtained from the same set of samples, show that the S(2) --> S(3) transition, in contrast to the S(0) --> S(1) and S(1) --> S(2) transitions, does not involve a Mn-centered oxidation. On the basis of new structural data from the S(3)-state, manganese mu-oxo bridge radical formation is proposed for the S(2) --> S(3) transition, and three possible mechanisms for the O-O bond formation are presented.

Spectroscopic study of the light-harvesting protein C-phycocyanin associated with colorless linker peptides

C-Phycocyanin (PC) trimers associated with linker polypeptides were isolated from the phycobilisome (PBS) rods of Synechococcus sp. PCC 7002. LXY refers to a linker polypeptide (L) having an apparent mass of Y kDa, located at position X in the phycobilisome where X can be R (rod), C (core) or RC (rod-core junction). Measurements of the absorption, fluorescence and excitation anisotropy of PC trimer, PC.LR32.3 and PC.LRC28.5 complexes document the spectroscopic modulation of each linker polypeptide on the PC chromophores. The difference spectra between the PC trimer and the PC-linker complexes show that although the effect induced by the linker polypeptides is qualitatively similar in behavior, the extent of the modulation is greater in PC.LRC28.5. Measurements taken at 77 K show that a red-wavelength component of the PC trimer absorption-fluorescence spectra is the target of the linker's influence and that this component is altered to a greater extent by LRC28.5. In addition the 77 K absorbance of the PC trimer resolves band features that are consistent with an excitonic coupling interaction between neighboring alpha 84 and beta 84 chromophores. These band features are also evident in the absorbance of PC.LR32.3 but are absent in PC.LRC28.5 indicating that LRC28.5 may be perturbing the coupling interaction established in the PC trimer alpha 84-beta 84 chromophore pairs. Structurally, the linker polypeptide should disrupt the C3 symmetry in the central cavity of the associated phycobiliprotein and this asymmetric interaction should serve to guide the transfer of excitation energy along PBS rods toward the core elements.

High-resolution X-ray spectroscopy of rare events: a different look at local structure and chemistry

The combination of large-acceptance high-resolution X-ray optics with bright synchrotron sources permits quantitative analysis of rare events such as X-ray fluorescence from very dilute systems, weak fluorescence transitions or X-ray Raman scattering. Transition-metal Kbeta fluorescence contains information about spin and oxidation state; examples of the characterization of the Mn oxidation states in the oxygen-evolving complex of photosystem II and Mn-consuming spores from the marine bacillus SG- are presented. Weaker features of the Kbeta spectrum resulting from valence-level and 'interatomic' ligand to metal transitions contain detailed information on the ligand- atom type, distance and orientation. Applications of this spectral region to characterize the local structure of model compounds are presented. X-ray Raman scattering (XRS) is an extremely rare event, but also represents a unique technique to obtain bulk-sensitive low-energy (<600 eV) X-ray absorption fine structure (XAFS) spectra using hard (approximately 10 keV) X-rays. A photon is inelastically scattered, losing part of its energy to promote an electron into an unoccupied level. In many cases, the cross section is proportional to that of the corresponding absorption process yielding the same X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) features. XRS finds application for systems that defy XAFS analysis at low energies, e.g. liquids or highly concentrated complex systems, reactive compounds and samples under extreme conditions (pressure, temperature). Recent results are discussed.

[Brachial plexus. Long lasting neurological deficit following interscalene blockade of the brachial plexus]

An interscalene block of the brachial plexus was combined with general anaesthesia for repair of a complex chronic lesion of the shoulder. The localisation of the plexus with electro-stimulation and the injection of Bupivacain 0.5% were accomplished easily and without painful sensations. 48 hours later the block was still partially present. Paraesthesia and a sensory and motor innervation deficit affected mainly the dorsal fascicle, but also areas innervated by the median and lateral fascicles. The deficit did not completely disappear for 18 month. The cause could have been due to direct traumatisation during blockade or operation, toxic action of the injected substance (Bupivacain 0.5%, 30 ml), distension of the plexus, a cervical syndrome or an aseptic plexitis, although a definite determination is not possible. However, the pattern of the lesion and the lack of pain during localisation of the plexus and injection favour traumatisation during the acromioplasty.

Methyl-coenzyme M formation in methanogenic archaea. Involvement of zinc in coenzyme M activation

Methyl-coenzyme M (2-methylthioethane sulfonate) is the key intermediate of methane formation in methanogenic archaea. It is generated from coenzyme M (2-mercaptoethane sulfonate) in methyl transfer reactions catalyzed by proteins containing zinc. Here, we report that, for methyltransferase MtaA from Methanosarcina barkeri, the zinc is involved in coenzyme M activation. For the experiments an inactive MtaA apoprotein was obtained by heterologous overproduction in Escherichia coli grown in the presence of 2 mM EDTA. The apoprotein was found to react with zinc or cobalt to the fully active holoenzyme. Appoximately 1 mol of transition metal was bound per mol of protein. Upon incubation of the holoenzyme with coenzyme M approximately 1 mol of proton was released per mol of zinc or cobalt. Protons were not released upon incubation of the apoprotein with coenzyme M or of the holoprotein with other thiol compounds or with methyl-coenzyme M. The findings are interpreted as indicating that the role of the transition metal in MtaA is to lower the microscopic pKa of the thiol group of coenzyme M by coordination to the zinc, and thus to increase its nucleophilicity for methyl group attack. The pKZn2+ of MtaA was re-determined and found to be > 15 and not 9.6 as previously reported by us.

Parallelizable Bayesian tomography algorithms with rapid, guaranteed convergence

Bayesian tomographic reconstruction algorithms generally require the efficient optimization of a functional of many variables. In this setting, as well as in many other optimization tasks, functional substitution (FS) has been widely applied to simplify each step of the iterative process. The function to be minimized is replaced locally by an approximation having a more easily manipulated form, e.g., quadratic, but which maintains sufficient similarity to descend the true functional while computing only the substitute. We provide two new applications of FS methods in iterative coordinate descent for Bayesian tomography. The first is a modification of our coordinate descent algorithm with one-dimensional (1-D) Newton-Raphson approximations to an alternative quadratic which allows convergence to be proven easily. In simulations, we find essentially no difference in convergence speed between the two techniques. We also present a new algorithm which exploits the FS method to allow parallel updates of arbitrary sets of pixels using computations similar to iterative coordinate descent. The theoretical potential speed up of parallel implementations is nearly linear with the number of processors if communication costs are neglected.

Methanol:coenzyme M methyltransferase from Methanosarcina barkeri -- substitution of the corrinoid harbouring subunit MtaC by free cob(I)alamin

Methyl-coenzyme M formation from coenzyme M and methanol in Methanosarcina barkeri is catalysed by an enzyme system composed of three polypeptides MtaA, MtaB and MtaC, the latter of which harbours a corrinoid prosthetic group. We report here that MtaC can be substituted by free cob(I)alamin which is methylated with methanol in an MtaB-catalysed reaction and demethylated with coenzyme M in an MtaA-catalysed reaction. Methyl transfer from methanol to coenzyme M was found to proceed at a relatively high specific activity at micromolar concentrations of cob(I)alamin. This finding was surprising because the methylation of cob(I)alamin catalysed by MtaB alone and the demethylation of methylcob(III)alamin catalysed by MtaA alone exhibit apparent Km for cob(I)alamin and methylcob(III)alamin of above 1 mm. A possible explanation is that MtaA positively affects the MtaB catalytic efficiency and vice versa by decreasing the apparent Km for their corrinoid substrates. Activation of MtaA by MtaB was methanol-dependent. In the assay for methanol:coenzyme M methyltransferase activity cob(I)alamin could be substituted by cob(I)inamide which is devoid of the nucleotide loop. Substitution was, however, only possible when the assays were supplemented with imidazole: approximately 1 mm imidazole being required for half-maximal activity. Methylation of cob(I)inamide with methanol was found to be dependent on imidazole but not on the demethylation of methylcob(III)inamide with coenzyme M. The demethylation reaction was even inhibited by imidazole. The structure and catalytic mechanism of the MtaABC complex are compared with the cobalamin-dependent methionine synthase.

His84 rather than His35 is the active site histidine in the corrinoid protein MrtA of the energy conserving methyltransferase complex from Methanobacterium thermoautotrophicum

The energy conserving corrinoid containing MtrA-H complex from Methanobacterium thermoautotrophicum is composed of eight different subunits of which MtrA harbors the corrinoid prosthetic group, the corrinoid being bound in the base-off/His-on configuration. Based on sequence comparisons it was recently proposed that His35 of MtrA is the active site histidine. We report here that His84 rather than His35 is the axial ligand to the cobamide in MtrA.

Tetramethylammonium:coenzyme M methyltransferase system from methanococcoides sp

A methanogen (strain NaT1) that belongs to the family of Methanosarcinaceae and that can grow on tetramethylammonium as the sole energy source has recently been isolated. We report here that cell extracts of the archaeon catalyze the formation of methyl-coenzyme M from coenzyme M and tetramethylammonium. The activity was dependent on the presence of Ti(III) citrate and ATP, and was rapidly lost under oxic conditions. Anoxic chromatography on DEAE-Sepharose revealed that two fractions, fractions 3 and 4, were required for activity. A 50-kDa protein that together with fraction 3 catalyzed methyl-coenzyme M formation from tetramethylammonium and coenzyme M was purified from fraction 4. From fraction 3, a 22-kDa corrinoid protein and a 40-kDa protein exhibiting methylcobalamin:coenzyme M methyltransferase (MT2) activity were purified. The N-terminal amino acid sequences of these purified proteins were determined. The 40-kDa protein showed sequence similarity to MT2 isoenzymes from Methanosarcina barkeri. Cell extract of strain NaT1 grown on trimethylamine rather than on tetramethylammonium did not exhibit tetramethylammonium:coenzyme M methyltransferase activity. The strain was identified as belonging to the genus of Methanococcoides, its closest relative being Methanococcoides methylutens.

Sulfur K-edge x-ray absorption spectroscopy: a spectroscopic tool to examine the redox state of S-containing metabolites in vivo

The sulfur K-edge x-ray absorption spectra for the amino acids cysteine and methionine and their corresponding oxidized forms cystine and methionine sulfoxide are presented. Distinct differences in the shape of the edge and the inflection point energy for cysteine and cystine are observed. For methionine sulfoxide the inflection point energy is 2.8 eV higher compared with methionine. Glutathione, the most abundant thiol in animal cells, also has been investigated. The x-ray absorption near-edge structure spectrum of reduced glutathione resembles that of cysteine, whereas the spectrum of oxidized glutathione resembles that of cystine. The characteristic differences between the thiol and disulfide spectra enable one to determine the redox status (thiol to disulfide ratio) in intact biological systems, such as unbroken cells, where glutathione and cyst(e)ine are the two major sulfur-containing components. The sulfur K-edge spectra for whole human blood, plasma, and erythrocytes are shown. The erythrocyte sulfur K-edge spectrum is similar to that of fully reduced glutathione. Simulation of the plasma spectrum indicated 32% thiol and 68% disulfide sulfur. The whole blood spectrum can be simulated by a combination of 46% disulfide and 54% thiol sulfur.

Methanol:coenzyme M methyltransferase from Methanosarcina barkeri--identification of the active-site histidine in the corrinoid-harboring subunit MtaC by site-directed mutagenesis

The enzyme system catalyzing the formation of methyl-coenzyme M from methanol and coenzyme M in Methanosarcina barkeri is composed of the three different polypeptides MtaA, MtaB and MtaC of which MtaC harbors a corrinoid prosthetic group. The heterologous expression of mtaA and mtaB in Escherichia coli has been described previously. We report here on the overproduction of the apoprotein of MtaC in E. coli, on its reconstitution to the active holoprotein with either cob(II)alamin or methyl-cob(III)alamin, and on the properties of the reconstituted corrinoid protein. Reconstituted MtaC was found to contain 1 mol bound cobamide/mol. EPR spectroscopic evidence is presented for a His residue as an axial ligand to Co2+ of the bound corrinoid. This active-site His was identified by site-directed mutagenesis as His136 in the MtaC sequence that contains four His residues. The reconstituted MtaC, in the cob(I)amide oxidation state, was methylated with methanol in the presence of MtaB and demethylated with coenzyme M in the presence of MtaA. In the presence of both MtaB and MtaA, methyl-coenzyme M was formed from methanol and coenzyme M at specific rates comparable to those determined for the enzyme system purified from M. barkeri. M. barkeri contains an isoenzyme of MtaA designated MtbA. The isoenzyme reacted with MtaC with only 2.5% of the activity of MtaA.

The role of cyclin E in the regulation of entry into S phase

Cyclin E is a crucial regulator of entry into S phase in higher eukaryotes and acts in association with the protein kinase cdk2. Cyclin E expression is transcriptionally controlled in mammalian cells resulting in a maximum just before entry into S phase. Premature expression of cyclin E advances entry into S phase, while lack of cyclin E prevents entry into S phase. Cyclin E/cdk2 activity is regulated at multiple levels (by transcription, phosphorylation and inhibitor proteins) and appears to be involved in triggering initiation of DNA replication and in regulating genes important for proliferation and progression through S phase.

Enhancement of synaptic excitation by GABAA receptor antagonists in rat embryonic midbrain culture

Alterations of synaptic excitation induced by exposure to gamma-aminobutyric acid-A (GABAA) receptor antagonists were investigated employing tight-seal whole cell recording from single neurons or pairs of neurons in rat embryonic midbrain culture. Application of GABAA receptor antagonists led to sustained depolarizations followed by synchronous paroxysmal depolarization shifts (PDSs). PDSs induced a transient increase in miniature excitatory postsynaptic currents in the presence as well as in the absence of a N-methyl-aspartate receptor antagonist. The increase in glutamate release supports the excitatory drive required to reinitiate PDSs from the quiescent interburst intervals. After washout of GABAA receptor antagonists, synaptic activity remained grouped, regardless of the presence or absence of PDS blockade by tetrodotoxin (TTX). Impediment of action potential-triggered transmitter release by Cd2+ or TTX also induced grouped activity. We conclude that changes in synaptic excitation are produced by the impaired GABAA inhibition per se and by the initiation of PDSs.

ML parameter estimation for Markov random fields with applications to Bayesian tomography

Markov random fields (MRF's) have been widely used to model images in Bayesian frameworks for image reconstruction and restoration. Typically, these MRF models have parameters that allow the prior model to be adjusted for best performance. However, optimal estimation of these parameters(sometimes referred to as hyper parameters) is difficult in practice for two reasons: i) direct parameter estimation for MRF's is known to be mathematically and numerically challenging; ii)parameters can not be directly estimated because the true image cross section is unavailable.In this paper, we propose a computationally efficient scheme to address both these difficulties for a general class of MRF models,and we derive specific methods of parameter estimation for the MRF model known as generalized Gaussian MRF (GGMRF).The first section of the paper derives methods of direct estimation of scale and shape parameters for a general continuously valued MRF. For the GGMRF case, we show that the ML estimate of the scale parameter, sigma, has a simple closed-form solution, and we present an efficient scheme for computing the ML estimate of the shape parameter, p, by an off-line numerical computation of the dependence of the partition function on p.The second section of the paper presents a fast algorithm for computing ML parameter estimates when the true image is unavailable. To do this, we use the expectation maximization(EM) algorithm. We develop a fast simulation method to replace the E-step, and a method to improve parameter estimates when the simulations are terminated prior to convergence.Experimental results indicate that our fast algorithms substantially reduce computation and result in good scale estimates for real tomographic data sets.

Methanol:coenzyme M methyltransferase from Methanosarcina barkeri. Zinc dependence and thermodynamics of the methanol:cob(I)alamin methyltransferase reaction

In Methanosarcina barkeri, methanogenesis from methanol is initiated by the formation of methyl-coenzyme M from methanol and coenzyme M. This methyl transfer reaction is catalyzed by two enzymes, designated methyltransferases 1 (MT1) and 2 (MT2). Transferase MT1, which is composed of a 50-kDa subunit, MtaB, and a 27-kDa corrinoid-harbouring subunit, MtaC, has been shown recently to catalyze the methylation of free cob(I)alamin with methanol [Sauer, K., Harms, U. & Thauer, R. K. (1997) Eur. J. Biochem. 243, 670-677]. We report here that this reaction is catalyzed by subunit MtaB overproduced in Escherichia coli. MtaB also catalyzed the formation of methanol from methylcobalamin and H2O, the hydrolysis being associated with a free-energy change deltaG(o)' of approximately +7.0 kJ/mol. MtaB was found to contain 1 mol zinc, and its activity to be zinc dependent (pK(Zn2+) = 9.3). The zinc dependence of the MT2 (MtaA)-catalyzed reaction is also described (pK(Zn2+) = 9.6).