Showing papers by "University of Konstanz published in 1998"
TL;DR: Sequence homologies and mutagenesis data are used to propose a structural mechanism for TonB-dependent siderophore-mediated transport across the outer membrane.
Abstract: FhuA, the receptor for ferrichrome-iron in Escherichia coli, is a member of a family of integral outer membrane proteins, which, together with the energy-transducing protein TonB, mediate the active transport of ferric siderophores across the outer membrane of Gram-negative bacteria. The three-dimensional structure of FhuA is presented here in two conformations: with and without ferrichrome-iron at resolutions of 2.7 and 2.5 angstroms, respectively. FhuA is a β barrel composed of 22 antiparallel β strands. In contrast to the typical trimeric arrangement found in porins, FhuA is monomeric. Located within the β barrel is a structurally distinct domain, the “cork,” which mainly consists of a four-stranded β sheet and four short α helices. A single lipopolysaccharide molecule is noncovalently associated with the membrane-embedded region of the protein. Upon binding of ferrichrome-iron, conformational changes are transduced to the periplasmic pocket of FhuA, signaling the ligand-loaded status of the receptor. Sequence homologies and mutagenesis data are used to propose a structural mechanism for TonB-dependent siderophore-mediated transport across the outer membrane.
780 citations
TL;DR: The authors empirically derive risk aversion functions implied by option prices and realized returns on the S&P 500 index simultaneously, showing that the risk aversion function dramatically change shape around the 1987 crash.
Abstract: A relationship exists between aggregate risk-neutral and subjective probability distributions and risk aversion functions. We empirically derive risk aversion functions implied by option prices and realized returns on the S&P 500 index simultaneously. These risk aversion functions dramatically change shapes around the 1987 crash: Precrash, they are positive and decreasing in wealth and largely consistent with standard economic theory. Postcrash, they are partially negative and partially increasing and irreconcilable with the theory. Mispricing in the option market is the most likely cause. A simulated trading strategy exploiting this mispricing shows excess returns even after accounting for the possibility of further crashes, transaction costs, and hedges against the downside risk.
643 citations
TL;DR: The maltose system of Escherichia coli offers an unusually rich set of enzymes, transporters, and regulators as objects of study, and basic issues that require clarification concerning the mechanism of MalT-mediated activation, repression by the transporter, biosynthesis and assembly of the outer membrane and inner membrane transporter proteins, and interrelationships between the mal enzymes and those of glucose and glycogen metabolism.
Abstract: The maltose system of Escherichia coli offers an unusually rich set of enzymes, transporters, and regulators as objects of study. This system is responsible for the uptake and metabolism of glucose polymers (maltodextrins), which must be a preferred class of nutrients for E. coli in both mammalian hosts and in the environment. Because the metabolism of glucose polymers must be coordinated with both the anabolic and catabolic uses of glucose and glycogen, an intricate set of regulatory mechanisms controls the expression of mal genes, the activity of the maltose transporter, and the activities of the maltose/maltodextrin catabolic enzymes. The ease of isolating many of the mal gene products has contributed greatly to the understanding of the structures and functions of several classes of proteins. Not only was the outer membrane maltoporin, LamB, or the phage lambda receptor, the first virus receptor to be isolated, but also its three-dimensional structure, together with extensive knowledge of functional sites for ligand binding as well as for phage λ binding, has led to a relatively complete description of this sugar-specific aqueous channel. The periplasmic maltose binding protein (MBP) has been studied with respect to its role in both maltose transport and maltose taxis. Again, the combination of structural and functional information has led to a significant understanding of how this soluble receptor participates in signaling the presence of sugar to the chemosensory apparatus as well as how it participates in sugar transport. The maltose transporter belongs to the ATP binding cassette family, and although its structure is not yet known at atomic resolution, there is some insight into the structures of several functional sites, including those that are involved in interactions with MBP and recognition of substrates and ATP. A particularly astonishing discovery is the direct participation of the transporter in transcriptional control of the mal regulon. The MalT protein activates transcription at all mal promoters. A subset also requires the cyclic AMP receptor protein for transcription. The MalT protein requires maltotriose and ATP as ligands for binding to a dodecanucleotide MalT box that appears in multiple copies upstream of all mal promoters. Recent data indicate that the ATP binding cassette transporter subunit MalK can directly inhibit MalT when the transporter is inactive due to the absence of substrate. Despite this wealth of knowledge, there are still basic issues that require clarification concerning the mechanism of MalT-mediated activation, repression by the transporter, biosynthesis and assembly of the outer membrane and inner membrane transporter proteins, and interrelationships between the mal enzymes and those of glucose and glycogen metabolism.
635 citations
TL;DR: In this article, the authors show that the domains of a phase-separating mixture of polymers in a thin film can be guided into arbitrary structures by a surface with a prepatterned variation of surface energies.
Abstract: Phase separation in bulk mixtures commonly leads to an isotropic, disordered morphology of the coexisting phases1. The presence of a surface can significantly alter the phase-separation process, however2,3. Here we show that the domains of a phase-separating mixture of polymers in a thin film can be guided into arbitrary structures by a surface with a prepatterned variation of surface energies. Such a pattern can be imposed on a surface by using printing methods for depositing microstructured molecular films4, thereby allowing for such patterns to be readily transferred to a two-component polymer film. This approach might provide a simple means for fabricating polymer-based microelectronic circuits5 or polymer resists for lithographic semiconductor processing.
549 citations
TL;DR: The mechanism whereby OxyS represses rpoS expression is examined and it is found that the OxyS RNA inhibits translation of the rPOS message, dependent on the hfq‐encoded RNA‐binding protein.
Abstract: The OxyS regulatory RNA integrates the adaptive response to hydrogen peroxide with other cellular stress responses and protects against DNA damage. Among the OxyS targets is the rpoS-encoded sigma(s) subunit of RNA polymerase. Sigma(s) is a central regulator of genes induced by osmotic stress, starvation and entry into stationary phase. We examined the mechanism whereby OxyS represses rpoS expression and found that the OxyS RNA inhibits translation of the rpoS message. This repression is dependent on the hfq-encoded RNA-binding protein (also denoted host factor I, HF-I). Co-immunoprecipitation and gel mobility shift experiments revealed that the OxyS RNA binds Hfq, suggesting that OxyS represses rpoS translation by altering Hfq activity.
443 citations
TL;DR: One general signalling mechanism used to transfer the information delivered by agonists into appropriate intracellular compartments involves the rapid redistribution of ionised calcium throughout the cell, which results in transient elevations of the cytosolic free Ca2+ concentration.
440 citations
TL;DR: In this paper, the authors found that there is a smaller distance between the representations of the digits in the affected hand of dystonic musicians than for the hands of non-musician control subjects.
Abstract: Focal hand dystonia involves a loss of motor control of one or more digits; it is associated with the repetitive, synchronous movements of the digits made by musicians over periods of many years. Magnetic source imaging revealed that there is a smaller distance (fusion) between the representations of the digits in somatosensory cortex for the affected hand of dystonic musicians than for the hands of non-musician control subjects. The data suggest that use-dependent susceptibility to digital representation fusion in cortex may be involved in the etiology of focal dystonia. A successful therapy for the condition has been developed based on this consideration.
420 citations
TL;DR: Following Nelson's (1996; Nelson & Narens, 1994) model of metacognition, it is suggested that goal intentions and, in particular, implementation intentions are important components of the metacognitive control of action geared toward its initiation, continuation, and termination.
Abstract: When people furnish their goal intentions (“I intend to attain the goal x!”) with implementation intentions (“I will initiate the goal-directed response y when situation z arises!”), the initiation of goal-directed responses becomes automatized. As this type of automaticity stems from a single act of will, it is referred to as strategic automaticity. We report various studies demonstrating that strategic automaticity leads to immediate and efficient responding, which does not need a conscious intent. In addition, the situational cues specified in implementation intentions seem to be easily detected and readily attended to. Further research indicates that the strategic automaticity induced by implementation intentions also helps resist temptations and fight bad habits. Following Nelson's (1996; Nelson & Narens, 1994) model of metacognition, we suggest that goal intentions and, in particular, implementation intentions are important components of the metacognitive control of action geared toward its initiati...
392 citations
TL;DR: A fusion protein between cyclophilin-D and glutathione S-transferase (GST) was shown to bind to purified liver inner mitochondrial membranes (IMMs) in a cyclosporin A (CsA)-sensitive manner and was enhanced by diamide treatment of the IMMs.
Abstract: A fusion protein between cyclophilin-D (CyP-D) and glutathione S-transferase (GST) was shown to bind to purified liver inner mitochondrial membranes (IMMs) in a cyclosporin A (CsA)-sensitive manner. Binding was enhanced by diamide treatment of the IMMs. Immobilized GST-CyP-D avidly bound a single 30 kDa protein present in Triton X-100-solubilized IMMs; immunoblotting showed this to be the adenine nucleotide translocase (ANT). Binding was prevented by pretreatment of the CyP-D with CsA, but not with cyclosporin H. Purified ANT also bound specifically to GST-CyP-D, but porin did not, even in the presence of ANT.
383 citations
TL;DR: In this paper, a review of x-ray photoelectron spectroscopy studies on carbon nitride (CN) is presented, based on results obtained from CN thin films prepared by mass selected ion-beam deposition.
Abstract: This paper reviews x-ray photoelectron spectroscopy studies on carbon nitride (CN) and reports on results obtained from CN thin films prepared by mass selected ion-beam deposition. The core-level spectra of samples deposited at room temperature show that nitrogen is incorporated into the amorphous network in two different bonding configurations; carbon has three main bonding configurations whose relative contributions vary as a function of the nitrogen content. For samples deposited at elevated temperatures an ordering of the amorphous CN network towards a crystalline graphitelike structure is observed. Furthermore, both deposition at elevated temperatures (350 \ifmmode^\circ\else\textdegree\fi{}C) and post-deposition ion irradiation have a strong influence on the bonding configuration in the CN films. Based on these results and the results reported in the reviewed literature a picture of the microstructure of carbon nitride deposited using energetic species is developed.
376 citations
TL;DR: It is shown that intracellular energy levels and mitochondrial function are rapidly compromised in necrosis, but not in apoptosis of neuronal cells, and that pre-empting human T cells of ATP switches the type of demise caused by two classic apoptotic triggers from apoptosis to necrosis.
TL;DR: In this article, the authors reported a which-way experiment in an atom interferometer in which the back action of path detection on the atom's momentum is too small to explain the disappearance of the interference pattern.
Abstract: The principle of complementarity refers to the ability of quantum-mechanical entities to behave as particles or waves under different experimental conditions. For example, in the famous double-slit experiment, a single electron can apparently pass through both apertures simultaneously, forming an interference pattern. But if a ‘which-way’ detector is employed to determine the particle's path, the interference pattern is destroyed. This is usually explained in terms of Heisenberg's uncertainty principle, in which the acquisition of spatial information increases the uncertainty in the particle's momentum, thus destroying the interference. Here we report a which-way experiment in an atom interferometer in which the ‘back action’ of path detection on the atom's momentum is too small to explain the disappearance of the interference pattern. We attribute it instead to correlations between the which-way detector and the atomic motion, rather than to the uncertainty principle.
TL;DR: It is concluded that artificial ventilation might cause pulmonary and systemic adverse reactions by inducing the release of mediators into the circulation.
Abstract: Artificial mechanical ventilation represents a major cause of iatrogenic lung damage in intensive care. It is largely unknown which mediators, if any, contribute to the onset of such complications. We investigated whether stress caused by artificial mechanical ventilation leads to induction, synthesis, and release of cytokines or eicosanoids from lung tissue. We used the isolated perfused and ventilated mouse lung where frequent perfusate sampling allows determination of mediator release into the perfusate. Hyperventilation was executed with either negative (NPV) or positive pressure ventilation (PPV) at a transpulmonary pressure that was increased 2.5-fold above normal. Both modes of hyperventilation resulted in an approximately 1.75-fold increased expression of tumor necrosis factor α (TNF α ) and interleukin-6 (IL-6) mRNA, but not of cyclooxygenase-2 mRNA. After switching to hyperventilation, prostacyclin release into the perfusate increased almost instantaneously from 19 ± 17 pg/ min to 230 ± 160 pg/m...
TL;DR: The inhibitory effect of N-methylVal-4-cyclosporin on the hexokinase complex may be explained by direct interaction with the creatine kinase dimer that appeared to support octamer formation.
TL;DR: In this article, a number of methods are presented for the efficient in situ detection of this substitution (i.e. in whole plants or in chloroplasts) while macroscopic observations point to the formation of heavy metal chlorophylls at higher concentrations, fluorescence microscopy enables the detection of the reaction at very low substitution rates Therefore, the course of this reaction can be followed by continuously measuring the fluorescence of whole plants Furthermore absorbance spectroscopy of whole cells or isolated chloroplast also enables the in situ detecting of heavy-metal chlorophyLLs.
Abstract: The in vivo substitution of magnesium, the central atom of chlorophyll, by heavy metals (mercury, copper, cadmium, nickel, zinc, lead) leads to a breakdown in photosynthesis and is an important damage mechanism in heavy metal-stressed plants In this study, a number of methods are presented for the efficient in situ detection of this substitution (ie in whole plants or in chloroplasts) While macroscopic observations point to the formation of heavy metal chlorophylls at higher concentrations, fluorescence microscopy enables the detection of this reaction at very low substitution rates Therefore, the course of the reaction can be followed by continuously measuring the fluorescence of whole plants Furthermore absorbance spectroscopy of whole cells or isolated chloroplasts also enables the in situ detection of heavy metal chlorophylls These methods provide practicable approaches in detecting the formation of these compounds in situ, avoiding artefacts that might occur using extraction methods based on polar solvents In addition to the new methods for in situ detection, an extreme heterogeneity in the reaction of cells in the same tissue upon heavy metal stress was observed: while some cells are already disintegrating, others still show normal fluorescence and photosynthetic activity Measurements of fluorescence kinetics gave a further hint that in high light intensity a substitution of Mg by heavy metals might take place specifically in PS II reaction centres
TL;DR: An increased rate of cell death in the adult nervous system underlies neurodegenerative disease and specific death mechanisms, based on specific neuronal characteristics such as excitability and the presence of specific channels or enzymes, have been unraveled in the brain.
TL;DR: In this article, the relation between mental and manual rotation was investigated in two experiments and the results suggest that mental object rotation and rotatory object manipulation share a common process that is thought to control the dynamics of both imagined and actually performed object reorientation.
Abstract: The relation between mental and manual rotation was investigated in 2 experiments. Experiment 1 compared the response times (RTs) of mental rotation about 4 axes in space with the RTs shown in the same task when participants were allowed to reorient the stimuli by means of rotational hand movements. For the 3 Cartesian axes, RT functions were quantitatively indistinguishable. Experiment 2 investigated interference between mental rotation and 4 kinds of simultaneously executed hand movements that did not reorient the stimuli. Interference was observed only when axes of manual and mental rotation coincided in space. Regardless of the hand used, concordant rotational directions facilitated, whereas discordant directions inhibited, mental rotation. The results suggest that mental object rotation and rotatory object manipulation share a common process that is thought to control he dynamics of both imagined and actually performed object reorientation.
TL;DR: The build-up of cortical facilitation reflected in SSVEP amplitude was found to bear a close temporal relationship with the emergence of accurate target discriminations at the newly attended location.
Abstract: Adaptive behavior requires the rapid switching of attention among potentially relevant stimuli that appear in the environment. The present study used an electrophysiological approach to continuously measure the time course of visual pathway facilitation in human subjects as attention was shifted from one location to another. Steady-state visual evoked potentials (SSVEPs) were recorded to rapidly flickering lights at attended and unattended locations, and variations in SSVEP amplitude over time were calculated after a cue to shift attention. The build-up of cortical facilitation reflected in SSVEP amplitude was found to bear a close temporal relationship with the emergence of accurate target discriminations at the newly attended location.
TL;DR: Sensory discrimination was normal and mislocalization (referral of stimulation-induced sensation to a phantom limb) was absent in the congenital amputees and the role of peripheral and central factors in the understanding of phantom limb pain and phantom limb phenomena is discussed.
Abstract: The relationship between phantom limb phenomena and cortical reorganization was examined in five subjects with congenital absence of an upper limb and nine traumatic amputees. Neuromagnetic source imaging revealed minimal reorganization of primary somatosensory cortex in the congenital amputees (M=0.69 cm, SD 0.24) and the traumatic amputees without phantom limb pain (M=0.27 cm, SD 0.25); the amputees with phantom limb pain showed massive cortical reorganization (M=2.22 cm, SD 0.78). Phantom limb pain and nonpainful phantom limb phenomena were absent in the congenital amputees. Whereas phantom limb pain was positively related to cortical reorganization (r=0.87), nonpainful phantom phenomena were not significantly correlated with cortical reorganization (r=0.34). Sensory discrimination was normal and mislocalization (referral of stimulation-induced sensation to a phantom limb) was absent in the congenital amputees. The role of peripheral and central factors in the understanding of phantom limb pain and phantom limb phenomena is discussed in view of these findings.
TL;DR: A source analysis indicated that the source current densities for the SSVEP attention effect had a focal origin in the contralateral parieto-occipital cortex.
TL;DR: In this article, the authors studied the antiferromagnetic correlations in the single layer system La{sub 2{minus}x}Sr {sub x}CuO{sub 4} and the bilayer system Y{sub 1{minus]x}Ca {sub X}Ba{sub 0}Cu{sub 3} O{sub 6}.
Abstract: By zero field muon spin rotation we studied the antiferromagnetic correlations in the single layer system La{sub 2{minus}x}Sr {sub x}CuO{sub 4} and the bilayer system Y{sub 1{minus}x}Ca {sub x}Ba{sub 2}Cu{sub 3}O{sub 6} . We observe a common phase diagram as a function of hole doping per plane with two distinct transitions in the magnetic ground state. The first transition marks the border between the 3D antiferromagnetic state and a disordered state with short ranged correlations. The second transition marks a distinct change in the magnetic correlations at the onset of superconductivity. {copyright} {ital 1998} {ital The American Physical Society}
TL;DR: Magnetic source imaging indicated that the cortical somatosensory representation of the fingers was frequently topographically disordered in blind Braille readers; in addition, they frequently misperceived which of these fingers was being touched by a light tactile stimulus.
Abstract: The mature mammalian nervous system alters its functional organization in a use-dependent manner. Enhanced stimulation of a body part enlarges its cortical representational zones and may change its topographic order. Little is known about the perceptual and behavioral relevance of these plastic alterations in cortical organization. We used blind Braille readers who use several fingers on each hand and who do so for many hours each day as a model to investigate this issue. Magnetic source imaging indicated that the cortical somatosensory representation of the fingers was frequently topographically disordered in these subjects; in addition, they frequently misperceived which of these fingers was being touched by a light tactile stimulus. In contrast, neither the disordered representation nor mislocalizations were observed in sighted controls. Blind non-teacher Braille readers who used only one finger for reading were not significantly different from the sighted controls. Thus, use-dependent cortical reorganization can be associated with functionally relevant changes in the perceptual and behavioral capacities of the individual.
TL;DR: The ability to oxidize ferrous iron anaerobically with nitrate at approximately pH 7 appears to be a widespread capacity among mesophilic denitrifying bacteria.
Abstract: Nine out of ten anaerobic enrichment cultures inoculated with sediment samples from various freshwater, brackish-water, and marine sediments exhibited ferrous iron oxidation in mineral media with nitrate and an organic cosubstrate at pH 7.2 and 30° C. Anaerobic nitrate-dependent ferrous iron oxidation was a biological process. One strain isolated from brackish-water sediment (strain HidR2, a motile, nonsporeforming, gram-negative rod) was chosen for further investigation of ferrous iron oxidation in the presence of acetate as cosubstrate. Strain HidR2 oxidized between 0.7 and 4.9 mM ferrous iron aerobically and anaerobically at pH 7.2 and 30° C in the presence of small amounts of acetate (between 0.2 and 1.1 mM). The strain gained energy for growth from anaerobic ferrous iron oxidation with nitrate, and the ratio of iron oxidized to acetate provided was constant at limiting acetate supply. The ability to oxidize ferrous iron anaerobically with nitrate at approximately pH 7 appears to be a widespread capacity among mesophilic denitrifying bacteria. Since nitrate-dependent iron oxidation closes the iron cycle within the anoxic zone of sediments and aerobic iron oxidation enhances the reoxidation of ferrous to ferric iron in the oxic zone, both processes increase the importance of iron as a transient electron carrier in the turnover of organic matter in natural sediments.
TL;DR: In this article, the authors demonstrate the absence of caveolae in (anti-caveolin negative) neurons and show anti-reggie-1 immunogold-labeled clusters at the plasmamembrane of DRGs.
Abstract: Neurons are believed to possess plasmalemmal microdomains and proteins analogous to the caveolae and caveolin of nonneuronal cells. Caveolae are plasmalemmal invaginations where activated glycosyl-phosphatidylinositol (GPI)-anchored proteins preferentially assemble and where transmembrane signaling may occur. Molecular cloning of rat reggie-1 and -2 (80% identical to goldfish reggie proteins) shows that reggie-2 is practically identical to mouse flotillin-1. Flotillin-1 and epidermal surface antigen (ESA) (flotillin-2) are suggested to represent possible membrane proteins in caveolae. Rat reggie-1 is 99% homologous to ESA in overlapping sequences but has a 49-amino-acid N-terminus not present in ESA. Antibodies (ABs) which recognize reggie-1 or -2 reveal that both proteins cluster at the plasmamembrane and occur in micropatches in neurons [dorsal root ganglia (DRGs), retinal ganglion, and PC-12 cells] and in nonneuronal cells. In neurons, reggie micropatches occur along the axon and in lamellipodia and filopodia of growth cones, but they do not occur in caveolae. By quantitative electronmicroscopic analysis we demonstrate the absence of caveolae in (anti-caveolin negative) neurons and show anti-reggie-1 immunogold-labeled clusters at the plasmamembrane of DRGs. When ABs against the GPI-anchored cell adhesion molecules (CAMs) F3 and Thy-1 are applied to live DRGs, the GPI-linked CAMs sequester into micropatches. Double immunofluorescence shows a colocalization of the CAMs with micropatches of anti-reggie antibodies. Thus, reggie-1 and reggie-2 identify sites where activated GPI-linked CAMs preferentially accumulate and which may represent noncaveolar micropatches (domains).
TL;DR: In this paper, the effects of variation in an irrelevant stimulus dimension on judgments of faces with respect to a relevant dimension were investigated, and the results suggest asymmetric dependencies between different components of face perception.
Abstract: Effects of variation in an irrelevant stimulus dimension on judgments of faces with respect to a relevant dimension were investigated. Dimensions were identity, emotional expression, and facial speech. The irrelevant dimension was correlated with, constant, or orthogonal to the relevant one. Reaction times (RTs) were predicted to increase over these conditions to the extent that the relevant dimension could not be processed independently of the irrelevant one. RTs for identity judgments were independent of variation in expression or facial speech, but RTs for expression and facial speech judgments were influenced by identity variation. Facial speech perception was affected by identity even when variation in the mouth region was eliminated. Moreover, observers could judge speech faster for personally familiar faces than for unfamiliar faces. The results suggest asymmetric dependencies between different components of face perception. Identity is perceived independently of, but may exert an influence on, expression and facial speech analysis.
TL;DR: Termite hindguts have long been considered simply to be anoxic fermentors, similar to the rumen of cattle, but this concept was challenged by recent investigations employing microsensor techniques, which demonstrated that the metabolic activity of the gut microbiota maintains steep oxygen and hydrogen gradients within the gut lumen.
TL;DR: Mutational analysis of the transmembrane helix, together with the additive regulatory effects of coexpression of both SLN and phospholamban (PLN) with SERCA1, provided evidence for different mechanisms of interaction of SLN
TL;DR: Mi‐CK octamers, together with CK substrates have a marked stabilizing and protective effect against mitochondrial permeability transition pore opening, thus providing a rationale for creatine supplementation of patients with neuromuscular and neurodegenerative diseases.
Abstract: Creatine kinase (CK) isoenzymes, specifically located at places of energy demand and energy production, are linked by a phosphocreatine/creatine (PCr/Cr) circuit, found in cells with intermittently high energy demands. Cytosolic CKs, in close conjunction with Ca 2+ -pumps, play a crucial role for the energetics of Ca 2+ -homeostasis. Mitochondrial Mi-CK, a cuboidal- shaped octamer with a central channel, binds and crosslinks mitochondrial membranes and forms a functionally coupled mi- crocompartment with porin and adenine nucleotide translocase for vectorial export of PCr into the cytosol. The CK system is regulated by AMP-activated protein kinase via PCr/Cr and ATP/AMP ratios. Mi-CK stabilizes and cross-links cristae- or in- ner/outer membranes to form parallel membrane stacks and, if overexpressed due to creatine depletion or cellular energy stress, forms those crystalline intramitochondrial inclusions seen in some mitochondrial cytopathy patients. Mi-CK is a prime target for free radical damage by peroxynitrite. Mi-CK octamers, together with CK substrates have a marked stabilizing and protective effect against mitochondrial permeability transition pore opening, thus providing a rationale for creatine supplementation of patients with neuromuscular and neurodegenerative diseases.
TL;DR: The X-ray structure of a sucrose-specific porin (ScrY) from Salmonella typhimurium has been determined by multiple isomorphous replacement at 2.4 Å resolution both in its uncomplexed form and with bound sucrose.
Abstract: The X-ray structure of a sucrose-specific porin (ScrY) from Salmonella typhimurium has been determined by multiple isomorphous replacement at 2.4 A resolution both in its uncomplexed form and with bound sucrose. ScrY is a noncrystallographic trimer of identical subunits, each with 413 structurally well-defined amino acids. A monomer is built up of 18 anti-parallel β-strands surrounding a hydrophilic pore, with a topology closely similar to that of maltoporin. Two non-overlapping sucrose-binding sites were identified in difference Fourier maps. The higher permeability for sucrose of ScrY as compared to maltoporin is mainly accounted for by differences in their pore-lining residues.
TL;DR: In addition to iron-reducing bacteria, fermenting bacteria are also capable of channeling electrons from anaerobic oxidations via humic acids towards iron reduction, indicating that future studies of electron flow in soils and sediments should be considered.
Abstract: Iron-reducing bacteria have been reported to reduce humic acids and low-molecular-weight quinones with electrons from acetate or hydrogen oxidation. Due to the rapid chemical reaction of amorphous ferric iron with the reduced reaction products, humic acids and low-molecular-weight redox mediators may play an important role in biological iron reduction. Since many anaerobic bacteria that are not able to reduce amorphous ferric iron directly are known to transfer electrons to other external acceptors, such as ferricyanide, 2,6-anthraquinone disulfonate (AQDS), or molecular oxygen, we tested several physiologically different species of fermenting bacteria to determine their abilities to reduce humic acids. Propionibacterium freudenreichii, Lactococcus lactis, and Enterococcus cecorum all shifted their fermentation patterns towards more oxidized products when humic acids were present; P. freudenreichii even oxidized propionate to acetate under these conditions. When amorphous ferric iron was added to reoxidize the electron acceptor, humic acids were found to be equally effective when they were added in substoichiometric amounts. These findings indicate that in addition to iron-reducing bacteria, fermenting bacteria are also capable of channeling electrons from anaerobic oxidations via humic acids towards iron reduction. This information needs to be considered in future studies of electron flow in soils and sediments.