bluuebunny/crossref_metadata_2025 huggingface dataset:
Intermedin (adrenomedullin‐2): a novel counter‐regulatory peptide in the cardiovascular and renal systems
Authors: Bell D , McDermott B J
Published: October 2007

Intermedin (IMD) is a novel peptide related to calcitonin gene‐related peptide (CGRP) and adrenomedullin (AM). Proteolytic processing of a larger precursor yields a series of biologically active C‐terminal fragments, IMD1–53, IMD1–47 and IMD8–47. IMD shares a family of receptors with AM and CGRP composed of a calcitonin‐receptor like receptor (CALCRL) associated with one of three receptor activity modifying proteins (RAMP). Compared to CGRP, IMD is less potent at CGRP1 receptors but more potent at AM1 receptors and AM2 receptors; compared to AM, IMD is more potent at CGRP1 receptors but less potent at AM1 and AM2 receptors. The cellular and tissue distribution of IMD overlaps in some aspects with that of CGRP and AM but is distinct from both. IMD is present in neonatal but absent or expressed sparsely, in adult heart and vasculature and present at low levels in plasma. The prominent localization of IMD in hypothalamus and pituitary and in kidney is consistent with a physiological role in the central and peripheral regulation of the circulation and water‐electrolyte homeostasis. IMD is a potent systemic and pulmonary vasodilator, influences regional blood flow and augments cardiac contractility. IMD protects myocardium from the deleterious effects of oxidative stress associated with ischaemia‐reperfusion injury and exerts an anti‐growth effect directly on cardiomyocytes to oppose the influence of hypertrophic stimuli. The robust increase in expression of the peptide in hypertrophied and ischaemic myocardium indicates an important protective role for IMD as an endogenous counter‐regulatory peptide in the heart.

British Journal of Pharmacology (2008) 153, S247–S262; doi:10.1038/sj.bjp.0707494; published online 29 October 2007
Differential effects of cannabinoid receptor agonists on regional brain activity using pharmacological MRI
Authors: Chin C‐L , Tovcimak A E , Hradil V P , Seifert T R , Hollingsworth P R , Chandran P , Zhu C Z , Gauvin D , Pai M , Wetter J , Hsieh G C , Honore P , Frost J M , Dart M J , Meyer M D , Yao B B , Cox B F , Fox G B
Published: October 2007

Background and purpose:

Activation of cannabinoid CB1 and/or CB2 receptors mediates analgesic effects across a broad spectrum of preclinical pain models. Selective activation of CB2 receptors may produce analgesia without the undesirable psychotropic side effects associated with modulation of CB1 receptors. To address selectivity in vivo, we describe non‐invasive, non‐ionizing, functional data that distinguish CB1 from CB2 receptor neural activity using pharmacological MRI (phMRI) in awake rats.

Experimental approach:

Using a high field (7 T) MRI scanner, we examined and quantified the effects of non‐selective CB1/CB2 (A‐834735) and selective CB2 (AM1241) agonists on neural activity in awake rats. Pharmacological specificity was determined using selective CB1 (rimonabant) or CB2 (AM630) antagonists. Behavioural studies, plasma and brain exposures were used as benchmarks for activity in vivo.

Key results:

The non‐selective CB1/CB2 agonist produced a dose‐related, region‐specific activation of brain structures that agrees well with published autoradiographic CB1 receptor density binding maps. Pretreatment with a CB1 antagonist but not with a CB2 antagonist, abolished these activation patterns, suggesting an effect mediated by CB1 receptors alone. In contrast, no significant changes in brain activity were found with relevant doses of the CB2 selective agonist.

Conclusion and implications:

These results provide the first clear evidence for quantifying in vivo functional selectivity between CB1 and CB2 receptors using phMRI. Further, as the presence of CB2 receptors in the brain remains controversial, our data suggest that if CB2 receptors are expressed, they are not functional under normal physiological conditions.

British Journal of Pharmacology (2008) 153, 367–379; doi:10.1038/sj.bjp.0707506; published online 29 October 2007
Potentiation of E‐4031‐induced torsade de pointes by HMR1556 or ATX‐II is not predicted by action potential short‐term variability or triangulation
Authors: Michael G , Dempster J , Kane K A , Coker S J
Published: October 2007

Background and purpose:

Torsade de pointes (TdP) can be induced by a reduction in cardiac repolarizing capacity. The aim of this study was to assess whether I
Ks blockade or enhancement of I
Na could potentiate TdP induced by I
Kr blockade and to investigate whether short‐term variability (STV) or triangulation of action potentials preceded TdP.

Experimental approach:

Experiments were performed in open‐chest, pentobarbital‐anaesthetized, α1‐adrenoceptor‐stimulated, male New Zealand White rabbits, which received three consecutive i.v. infusions of either the I
Kr blocker E‐4031 (1, 3 and 10 nmol kg−1 min−1), the I
Ks blocker HMR1556 (25, 75 and 250 nmol kg−1 min−1) or E‐4031 and HMR1556 combined. In a second study rabbits received either the same doses of E‐4031, the I
Na enhancer, ATX‐II (0.4, 1.2 and 4.0 nmol kg−1) or both of these drugs. ECGs and epicardial monophasic action potentials were recorded.

Key results:

HMR1556 alone did not cause TdP but increased E‐4031‐induced TdP from 25 to 80%. ATX‐II alone caused TdP in 38% of rabbits, as did E‐4031; 75% of rabbits receiving both drugs had TdP. QT intervals were prolonged by all drugs but the extent of QT prolongation was not related to the occurrence of TdP. No changes in STV were detected and triangulation was only increased after TdP occurred.

Conclusions and implications:

Giving modulators of ion channels in combination substantially increased TdP but, in this model, neither STV nor triangulation of action potentials could predict TdP.

British Journal of Pharmacology (2007) 152, 1215–1227; doi:10.1038/sj.bjp.0707513; published online 29 October 2007
Δ9‐Tetrahydrocannabinol (THC) and AM 404 protect against cerebral ischaemia in gerbils through a mechanism involving cannabinoid and opioid receptors
Authors: Zani A , Braida D , Capurro V , Sala M
Published: October 2007

Background and purpose:

It has been suggested that the endocannabinoid system elicits neuroprotection against excitotoxic brain damage. In the present study the therapeutic potential of AM 404 on ischaemia‐induced neuronal injury was investigatedin vivoand compared with that of the classical cannabinoid receptor type 1 (CB1) agonist, Δ9‐tetraydrocannabinol (THC), using a model of transient global cerebral ischaemia in the gerbil.

Experimental approach:

The effects of AM 404 (0.015–2 mg kg−1) and THC (0.05–2 mg kg−1), given 5 min after ischaemia, were measured from 1 h to 7 days in terms of electroencephalographic (EEG) total spectral power, spontaneous motor activity, memory function, rectal temperature and hippocampal CA1neuronal count.

Key results:

Over the dose range tested, AM 404 (2 mg kg−1) and THC (1 mg kg−1) completely reversed the ischaemia‐induced behavioural, EEG and histological damage. Only THC (1 and 2 mg kg−1) induced a decrease of body temperature. Pretreatment with the selective CB1receptor antagonist, AM 251 (1 mg kg−1) and the opioid antagonist, naloxone (2 mg kg−1) reversed the protective effect induced by both AM 404 and THC while the TRPV1vanilloid antagonist, capsazepine (0.01 mg kg−1), was ineffective.

Conclusions and implications:

Our findings demonstrate that AM 404 and THC reduce neuronal damage caused by bilateral carotid occlusion in gerbils and that this protection is mediated through an interaction with CB1and opioid receptors. Endocannabinoids might form the basis for the development of new neuroprotective drugs useful for the treatment of stroke and other neurodegenerative pathologies.

British Journal of Pharmacology(2007)152, 1301–1311; doi:10.1038/sj.bjp.0707514; published online 29 October 2007
The endothelin system as a therapeutic target in cardiovascular disease: great expectations or bleak house?
Authors: Kirkby N S , Hadoke P W F , Bagnall A J , Webb D J
Published: October 2007

There is considerable evidence that the potent vasoconstrictor endothelin‐1 (ET‐1) contributes to the pathogenesis of a variety of cardiovascular diseases. As such, pharmacological manipulation of the ET system might represent a promising therapeutic goal. Many clinical trials have assessed the potential of ET receptor antagonists in cardiovascular disease, the most positive of which have resulted in the licensing of the mixed ET receptor antagonist bosentan, and the selective ETAreceptor antagonists, sitaxsentan and ambrisentan, for the treatment of pulmonary arterial hypertension (PAH). In contrast, despite encouraging data fromin vitroand animal studies, outcomes in human heart failure have been disappointing, perhaps illustrating the risk of extrapolating preclinical work to man. Many further potential applications of these compounds, including resistant hypertension, chronic kidney disease, connective tissue disease and sub‐arachnoid haemorrhage are currently being investigated in the clinic. Furthermore, experience from previous studies should enable improved trial design and scope remains for development of improved compounds and alternative therapeutic strategies. Although ET‐converting enzyme inhibitors may represent one such alternative, there have been relatively few suitable compounds developed, and consequently, clinical experience with these agents remains extremely limited. Recent advances, together with an increased understanding of the biology of the ET system provided by improved experimental tools (including cell‐specific transgenic deletion of ET receptors), should allow further targeting of clinical trials to diseases in which ET is involved and allow the therapeutic potential for targeting the ET system in cardiovascular disease to be fully realized.

British Journal of Pharmacology(2008)153, 1105–1119; doi:10.1038/sj.bjp.0707516; published online 29 October 2007
Cannabinoid receptors in acute and chronic complications of atherosclerosis
Authors: Mach F , Montecucco F , Steffens S
Published: October 2007

Atherosclerosis is a chronic inflammatory disease that is the primary cause of myocardial infarction and stroke, which occur after sudden thrombotic occlusion of an artery. A growing body of evidence suggests that cannabinoid signalling plays a fundamental role in atherosclerosis development and its clinical manifestations. Thus, CB2 receptors are protective in myocardial ischaemia/reperfusion and implicated in the modulation of chemotaxis, which is crucial for the recruitment of leukocytes during inflammation. Delta‐9‐Tetrahydrocannabinol (THC)‐mediated activation has been shown to inhibit atherosclerotic plaque progression in a CB2 dependent manner. Although CB1 and CB2 expression has been reported on platelets, their involvement in thrombus formation is still controversial. While several reports suggest that CB1 receptors may have a relevant role in neuroprotection after ischaemic stroke, recent studies show the protective effects in various forms of neuroprotection are not related to CB1 stimulation, and a protective role of CB1 blockade has also been reported. In addition, vascular and myocardial CB1 receptors contribute to the modulation of blood pressure and heart rate. It is tempting to suggest that pharmacological modulation of the endocannabinoid system is a potential novel therapeutic strategy in the treatment of atherosclerosis. For these purposes, it is important to better understand the complex mechanisms of endocannabinoid signalling and potential consequences of its pharmacological modulation, as it may have both pro‐ and anti‐atherosclerotic effects.

British Journal of Pharmacology (2008) 153, 290–298; doi:10.1038/sj.bjp.0707517; published online 29 October 2007
Role of Ca2+entry and Ca2+stores in atypical smooth muscle cell autorhythmicity in the mouse renal pelvis
Authors: Lang R J , Hashitani H , Tonta M A , Suzuki H , Parkington H C
Published: October 2007

Background and purpose:

Electrically active atypical smooth muscle cells (ASMCs) within the renal pelvis have long been considered to act as pacemaker cells driving pelviureteric peristalsis. We have investigated the role of Ca2+entry and uptake into and release from internal stores in the generation of Ca2+transients and spontaneous transient depolarizations (STDs) in ASMCs.

Experimental approach:

The electrical activity and separately visualized changes in intracellular Ca2+concentration in typical smooth muscle cells (TSMCs), ASMCs and interstitial cells of Cajal‐like cells (ICC‐LCs) were recorded using intracellular microelectrodes and a fluorescent Ca2+indicator, fluo‐4.

Results:

In 1 μMnifedipine, high frequency (10–30 min−1) Ca2+transients and STDs were recorded in ASMCs, while ICC‐LCs displayed low frequency (1–3 min−1) Ca2+transients. All spontaneous electrical activity and Ca2+transients were blocked upon removal of Ca2+from the bathing solution, blockade of Ca2+store uptake with cyclopiazonic acid (CPA) and with 2‐aminoethoxy‐diphenylborate (2‐APB). STD amplitudes were reduced upon removal of the extracellular Na+or blockade of IP3dependent Ca2+store release with neomycin or U73122. Blockade of ryanodine‐sensitive Ca2+release blocked ICC‐LC Ca2+transients but only reduced Ca2+transient discharge in ASMCs. STDs in ASMCS were also little affected by DIDS, La3+, Gd3+or by the replacement of extracellular Cl‐with isethionate.

Conclusions:

ASMCs generated Ca2+transients and cation‐selective STDs via mechanisms involving Ca2+release from IP3‐dependent Ca2+stores, STD stimulation of TSMCs was supported by Ca2+entry through L type Ca2+channels and Ca2+release from ryanodine‐sensitive stores.

British Journal of Pharmacology(2007)152, 1248–1259; doi:10.1038/sj.bjp.0707535; published online 29 October 2007
Relevance of anaesthesia for dofetilide‐induced torsades de pointes in α1‐adrenoceptor‐stimulated rabbits
Authors: Vincze D , Farkas A S , Rudas L , Makra P , Csík N , Leprán I , Forster T , Csanády M , Papp J G , Varró A , Farkas A
Published: October 2007

Background and purpose:

No information is available concerning the effects of anaesthetics in the most frequently used in vivo pro‐arrhythmia model. Accordingly, in this study we examined the effect of pentobarbital, propofol or α‐chloralose anaesthesia on the pro‐arrhythmic activity of the class III anti‐arrhythmic dofetilide in α1‐adrenoceptor‐stimulated rabbits.

Experimental approach:

Rabbits anaesthetized intravenously with pentobarbital, propofol or α‐chloralose were infused simultaneously with the α1‐adrenoceptor agonist phenylephrine (15 μg kg−1 min−1, i.v.) and dofetilide (0.04 mg kg−1 min−1, i.v.). The electrocardiographic QT interval, the T
peak–T
end interval and certain QT variability parameters were measured. The heart rate variability and the baroreflex sensitivity were utilized to assess the vagal nerve activity. The spectral power of the systolic arterial pressure was calculated in the frequency range 0.15–0.5 Hz to assess the sympathetic activity.

Key results:

Pentobarbital considerably reduced, whereas propofol did not significantly affect the incidence of dofetilide‐induced torsades de pointes (TdP) as compared with the results with α‐chloralose (40% (P=0.011) and 70% (P=0.211) vs 100%, respectively). In additional experiments, neither doubling of the rate of the dofetilide infusion nor tripling of the rate of phenylephrine infusion elevated the incidence of TdP to the level seen with α‐chloralose. None of the repolarization‐related parameters predicted TdP. The indices of the parasympathetic and sympathetic activity were significantly depressed in the α‐chloralose and propofol anaesthesia groups.

Conclusions and implications:

In rabbits, anaesthetics may affect drug‐induced TdP genesis differently, which must be considered when results of different studies are compared.

British Journal of Pharmacology (2008) 153, 75–89; doi:10.1038/sj.bjp.0707536; published online 29 October 2007
Effects of angiotensin II blockade on inflammation‐induced alterations of pharmacokinetics and pharmacodynamics of calcium channel blockers
Authors: Hanafy S , Dagenais N J , Dryden W F , Jamali F
Published: October 2007

Background and purpose:

Inflammation elevates plasma verapamil concentrations but diminishes pharmacological response. Angiotensin II is a pro‐inflammatory mediator. We examined the effect of angiotensin II receptor blockade on the pharmacokinetics and pharmacodynamics of verapamil, as well as the binding properties and amounts of its target protein in calcium channels, in a rat model of inflammation.

Experimental approach:

We used 4 groups of male Sprague–Dawley rats (220–280 g): inflamed‐placebo, inflamed‐treated, control‐placebo and control‐treated. Inflammation as pre‐adjuvant arthritis was induced by injecting Mycobacterium butyricum on day 0. From day 6 to 12, 30 mg kg−1 oral valsartan or placebo was administered twice daily. On day 12, a single oral dose of 25 mg kg−1 verapamil was administered and prolongation of the PR interval measured and plasma samples collected for verapamil and nor‐verapamil analysis. The amounts of the target protein Cav1.2 subunit of L‐type calcium channels in heart was measured by Western blotting and ligand binding with 3H‐nitrendipine.

Key results:

Inflammation reduced effects of verapamil, although plasma drug concentrations were increased. This was associated with a reduction in ligand binding capacity and amount of the calcium channel target protein in heart extracts. Valsartan significantly reversed the down‐regulating effect of inflammation on verapamil's effects on the PR interval, and the lower level of protein binding and the decreased target protein.

Conclusions and implications:

Reduced responses to calcium channel blockers in inflammatory conditions appeared to be due to a reduced amount of target protein that was reversed by the angiotensin II antagonist, valsartan.

British Journal of Pharmacology (2008) 153, 90–99; doi:10.1038/sj.bjp.0707538; published online 29 October 2007
Electromechanical characterization of cinnamophilin, a natural thromboxane A2 receptor antagonist with anti‐arrhythmic activity, in guinea‐pig heart
Authors: Chang G‐J , Su M‐J , Wu T‐S , Chen W‐P , Kuo C‐M
Published: October 2007

Background and purpose:

Cinnamophilin, a thromboxane A2 receptor antagonist, has been identified as a prominent anti‐arrhythmic agent in rat heart. This study aimed to determine its electromechanical and anti‐arrhythmic effects in guinea‐pig hearts.

Experimental approach:

Microelectrodes were used to study action potentials in ventricular papillary muscles. Fluo‐3 fluorimetric ratio and whole‐cell voltage‐clamp techniques were used to record calcium transients and membrane currents in single ventricular myocytes, respectively. Intracardiac electrocardiograms were obtained and the anti‐arrhythmic efficacy was determined from isolated perfused hearts.

Key results:

In papillary muscles, cinnamophilin decreased the maximal rate of upstroke (Vmax) and duration of action potential, and reduced the contractile force. In single ventricular myocytes, cinnamophilin reduced Ca2+ transient amplitude. Cinnamophilin decreased the L‐type Ca2+ current (ICa,L)(IC50=7.5 μM) with use‐dependency, induced a negative shift of the voltage‐dependent inactivation and retarded recovery from inactivation. Cinnamophilin also decreased the Na+ current (INa) (IC50=2.7 μM) and to a lesser extent, the delayed outward (IK), inward rectifier (IK1), and ATP‐sensitive (IK,ATP) K+ currents. In isolated perfused hearts, cinnamophilin prolonged the AV nodal conduction interval and Wenckebach cycle length and the refractory periods of the AV node, His‐Purkinje system and ventricle, while shortening the ventricular repolarization time. Additionally, cinnamophilin reduced the occurrence of reperfusion‐induced ventricular fibrillation.

Conclusions and implications:

These results suggest that the promising anti‐arrhythmic effect and the changes in the electromechanical function induced by cinnamophilin in guinea‐pig heart can be chiefly accounted for by inhibition of ICa,L and INa.

British Journal of Pharmacology (2008) 153, 110–123; doi:10.1038/sj.bjp.0707541; published online 29 October 2007
Effects of chronic in vivo administration of nitroglycerine on ACh‐induced endothelium‐dependent relaxation in rabbit cerebral arteries
Authors: Watanabe Y , Kusama N , Itoh T
Published: October 2007

Background and purpose:

In the setting of nitrate tolerance, endothelium‐dependent relaxation is reduced in several types of peripheral vessels. However, it is unknown whether chronic in vivo administration of nitroglycerine modulates such relaxation in cerebral arteries.

Experimental approach:

Isometric force and smooth muscle cell membrane potential were measured in endothelium‐intact strips from rabbit middle cerebral artery (MCA) and posterior cerebral artery (PCA).

Key results:

ACh (0.1–10 μM) concentration‐dependently induced endothelium‐dependent relaxation during the contraction induced by histamine in both MCA and PCA. Chronic (10 days) in vivo administration of nitroglycerine reduced the ACh‐induced relaxation in PCA but not in MCA, in the presence of the cyclooxygenase inhibitor diclofenac (3 μM). In the presence of the NO‐synthase inhibitor N
ω‐nitro‐L‐arginine (L‐NNA, 0.1 mM) plus diclofenac, in MCA from both nitroglycerine‐untreated control and ‐treated rabbits, ACh (0.1–10 μM) induced a smooth muscle cell hyperpolarization and relaxation, and these were blocked by the small‐conductance Ca2+‐activated K+‐channel inhibitor apamin (0.1 μM), but not by the large‐ and intermediate‐conductance Ca2+‐activated K+‐channel inhibitor charybdotoxin (0.1 μM). In contrast, in PCA, ACh (<3 μM) induced neither hyperpolarization nor relaxation under these conditions, suggesting that the endothelium‐derived relaxing factor is NO in PCA, whereas endothelium‐derived hyperpolarizing factor (EDHF) plays a significant role in MCA.

Conclusions and implications:

It is suggested that in rabbit cerebral arteries, the function of the endothelium‐derived relaxing factor NO and that of EDHF may be modulated differently by chronic in vivo administration of nitroglycerine.

British Journal of Pharmacology (2008) 153, 132–139; doi:10.1038/sj.bjp.0707562; published online 29 October 2007
A novel DNA helicase with strand-annealing activity from the crenarchaeon Sulfolobus solfataricus
Authors: De Felice Mariarita , Aria Valentina , Esposito Luca , De Falco Mariarosaria , Pucci Biagio , Rossi Mosè , Pisani Francesca M.
Published: October 2007

To protect their genetic material cells adopt different mechanisms linked to DNA replication, recombination and repair. Several proteins function at the interface of these DNA transactions. In the present study, we report on the identification of a novel archaeal DNA helicase. BlastP searches of the Sulfolobus solfataricus genome database allowed us to identify an open reading frame (SSO0112, 875 amino acid residues) having sequence similarity with the human RecQ5β. The corresponding protein, termed Hel112 by us, was produced in Escherichia coli in soluble form, purified to homogeneity and characterized. Gel-filtration chromatography and glycerol-gradient sedimentation analyses revealed that Hel112 forms monomers and dimers in solution. Biochemical characterization of the two oligomeric species revealed that only the monomeric form has an ATP-dependent 3′–5′ DNA-helicase activity, whereas, unexpectedly, both the monomeric and dimeric forms possess DNA strand-annealing capability. The Hel112 monomeric form is able to unwind forked and 3′-tailed DNA structures with high efficiency, whereas it is almost inactive on blunt-ended duplexes and bubble-containing molecules. This analysis reveals that S. solfataricus Hel112 shares some enzymatic features with the RecQ-like DNA helicases and suggests potential cellular functions of this protein.
Physical and functional interaction of FgFtr1–FgFet1 and FgFtr2–FgFet2 is required for iron uptake in Fusarium graminearum
Authors: Park Yong-Sung , Kim Ji-Hyun , Cho Jin-Hwa , Chang Hyo-Ihl , Kim Seung-Wook , Paik Hyun-Dong , Kang Chang-Won , Kim Tae-Hyoung , Sung Ha-Chin , Yun Cheol-Won
Published: October 2007

FgFtr1 and FgFtr2 are putative iron permeases, and FgFet1 and FgFet2 are putative ferroxidases of Fusarium graminearum. They have high homologies with iron permease ScFtr1 and ferroxidase ScFet3 of Saccharomyces cerevisiae at the amino acid level. The genes encoding iron permease and ferroxidase were localized to the same chromosome in the manner of FgFtr1/FgFet1 and FgFtr2/FgFet2. The GFP (green fluorescent protein)-fused versions of FgFtr1 and FgFtr2 showed normal functions when compared with FgFtr1 and FgFtr2 in an S. cerevisiae system, and the cellular localizations of FgFtr1 and FgFtr2 in S. cerevisiae depended on the expression of their putative ferroxidase partners FgFet1 and FgFet2 respectively. Although FgFtr1 was found on the plasma membrane when FgFet1 and FgFtr1 were co-transformed in S. cerevisiae, most of the FgFtr1 was found in the endoplasmic reticulum compartment when co-expressed with FgFet2. Furthermore, FgFtr2 was found on the vacuolar membrane when FgFet2 was co-expressed. From the two-hybrid analysis, we confirmed the interaction of FgFtr1 and FgFet1, and the same result was found between FgFtr2 and FgFet2. Iron-uptake activity also depended on the existence of the respective partner. Finally, the FgFtr1 and FgFtr2 were found on the plasma and vacuolar membrane respectively, in F. graminearum. Taken together, these results strongly suggest that FgFtr1 and FgFtr2 from F. graminearum encode the iron permeases of the plasma membrane and vacuolar membrane respectively, and require their specific ferroxidases to carry out normal function. Furthermore, the present study suggests that the reductive iron-uptake system is conserved from yeast to filamentous fungi.
Human wild-type alanine:glyoxylate aminotransferase and its naturally occurring G82E variant: functional properties and physiological implications
Authors: Cellini Barbara , Bertoldi Mariarita , Montioli Riccardo , Paiardini Alessandro , Borri Voltattorni Carla
Published: October 2007

Human hepatic peroxisomal AGT (alanine:glyoxylate aminotransferase) is a PLP (pyridoxal 5′-phosphate)-dependent enzyme whose deficiency causes primary hyperoxaluria Type I, a rare autosomal recessive disorder. To acquire experimental evidence for the physiological function of AGT, the Keq,overall of the reaction, the steady-state kinetic parameters of the forward and reverse reactions, and the pre-steady-state kinetics of the half-reactions of the PLP form of AGT with L-alanine or glycine and the PMP (pyridoxamine 5′-phosphate) form with pyruvate or glyoxylate have been measured. The results indicate that the enzyme is highly specific for catalysing glyoxylate to glycine processing, thereby playing a key role in glyoxylate detoxification. Analysis of the reaction course also reveals that PMP remains bound to the enzyme during the catalytic cycle and that the AGT–PMP complex displays a reactivity towards oxo acids higher than that of apoAGT in the presence of PMP. These findings are tentatively related to possible subtle rearrangements at the active site also indicated by the putative binding mode of catalytic intermediates. Additionally, the catalytic and spectroscopic features of the naturally occurring G82E variant have been analysed. Although, like the wild-type, the G82E variant is able to bind 2 mol PLP/dimer, it exhibits a significant reduced affinity for PLP and even more for PMP compared with wild-type, and an altered conformational state of the bound PLP. The striking molecular defect of the mutant, consisting in the dramatic decrease of the overall catalytic activity (∼0.1% of that of normal AGT), appears to be related to the inability to undergo an efficient transaldimination of the PLP form of the enzyme with amino acids as well as an efficient conversion of AGT–PMP into AGT–PLP. Overall, careful biochemical analyses have allowed elucidation of the mechanism of action of AGT and the way in which the disease causing G82E mutation affects it.
Investigation of the redox centres of periplasmic selenate reductase from Thauera selenatis by EPR spectroscopy
Authors: Dridge Elizabeth J. , Watts Carys A. , Jepson Brian J. N. , Line Kirsty , Santini Joanne M. , Richardson David J. , Butler Clive S.
Published: October 2007

Periplasmic SER (selenate reductase) from Thauera selenatis is classified as a member of the Tat (twin-arginine translocase)-translocated (Type II) molybdoenzymes and comprises three subunits each containing redox cofactors. Variable-temperature X-band EPR spectra of the purified SER complex showed features attributable to centres [3Fe–4S]1+, [4Fe–4S]1+, Mo(V) and haem-b. EPR-monitored redox-potentiometric titration of the SerABC complex (SerA–SerB–SerC, a hetero-trimetric complex of αβγ subunits) revealed that the [3Fe–4S] cluster (FS4, iron-sulfur cluster 4) titrated as n=1 Nernstian component with a midpoint redox potential (Em) of +118±10 mV for the [3Fe–4S]1+/0 couple. A [4Fe–4S]1+ cluster EPR signal developed over a range of potentials between 300 and −200 mV and was best fitted to two sequential Nernstian n=1 curves with midpoint redox potentials of +183±10 mV (FS1) and −51±10 mV (FS3) for the two [4Fe–4S]1+/2+ cluster couples. Upon further reduction, the observed signal intensity of the [4Fe–4S]1+ cluster decreases. This change in intensity can again be fitted to an n=1 Nernstian component with a midpoint potential (Em) of about −356 mV (FS2). It is considered likely that, at low redox potential (Em less than −300 mV), the remaining oxidized cluster is reduced (spin S=1/2) and strongly spin-couples to a neighbouring [4Fe–4S]1+ cluster rendering both centres EPR-silent. The involvement of both [3Fe–4S] and [4Fe–4S] clusters in electron transfer to the active site of the periplasmic SER was demonstrated by the re-oxidation of the clusters under anaerobic selenate turnover conditions. Attempts to detect a high-spin [4Fe–4S] cluster (FS0) in SerA at low temperature (5 K) and high power (100 mW) were unsuccessful. The Mo(V) EPR recorded at 60 K, in samples poised at pH 6.0, displays principal g values of g3∼1.999, g2∼1.996 and g1∼1.965 (gav 1.9867). The dominant features at g2 and g3 are not split, but hyperfine splitting is observed in the g1 region of the spectrum and can be best simulated as arising from a single proton with a coupling constant of A1 (1H)=1.014 mT. The presence of the haem-b moiety in SerC was demonstrated by the detection of a signal at g∼3.33 and is consistent with haem co-ordinated by methionine and lysine axial ligands. The combined evidence from EPR analysis and sequence alignments supports the assignment of the periplasmic SER as a member of the Type II molybdoenzymes and provides the first spectro-potentiometric insight into an enzyme that catalyses a key reductive reaction in the biogeochemical selenium cycle.
MARCKS-like protein, a membrane protein identified for its expression in developing neural retina, plays a role in regulating retinal cell proliferation
Authors: Zhao Jing , Izumi Tomonori , Nunomura Kazuto , Satoh Shinya , Watanabe Sumiko
Published: October 2007

Membrane proteins are expressed in a specific manner in developing tissues, and characterization of these proteins is valuable because it allows them to be used as cell surface markers. Furthermore, they are potentially important for the regulation of organogenesis because some may participate in signal transduction. In the present study, we used proteomics to examine the comprehensive protein expression profile of the membrane fraction in the embryonic and adult mouse retina. We purified the retinal membrane fraction by sucrose-density-gradient centrifugation and analysed total proteins using shotgun analysis on a nanoflow LC–MS/MS (liquid chromatography tandem MS) system. Approximately half of the 326 proteins from the adult retina and a quarter of the 310 proteins from the embryonic retina (day 17) appeared to be membrane-associated proteins. Among these, MLP [MARCKS (myristoylated alanine-rich C-kinase substrate)-like protein], which shares approx. 50% amino acid identity with MARCKS, was selected for further characterization. The mRNA and surface protein expression of MLP decreased as retinal development progressed. Overexpression of MLP by retrovirus-mediated gene transfer enhanced the proliferation of retinal progenitor cells without affecting differentiation or cell migration in a retinal explant culture system. In contrast, MLP overexpression did not promote proliferation in fibroblasts (NIH 3T3 cells). Mutation analysis of MLP demonstrated that myristoylation was necessary to promote proliferation and that phosphorylation inhibited proliferation, indicating the functional importance of membrane localization.
A role for NPC1 and NPC2 in intestinal cholesterol absorption – the hypothesis gutted
Authors: Liscum Laura
Published: October 2007

Dietary and biliary cholesterol are taken up by intestinal epithelial cells and transported to the endoplasmic reticulum. At the endoplasmic reticulum, cholesterol is esterified, packaged into chylomicrons and secreted into the lymph for delivery to the bloodstream. NPC1L1 (Niemann–Pick C1-like 1) is a protein on the enterocyte brush-border membrane that facilitates cholesterol absorption. Cholesterol's itinerary as it moves to the endoplasmic reticulum is unknown, as is the identity of any cellular proteins that facilitate the movement. Two proteins that play an important role in intracellular cholesterol transport and could potentially influence NPC1L1-mediated cholesterol uptake are NPC1 and NPC2 (Niemann–Pick type C disease proteins 1 and 2). In this issue of the Biochemical Journal, Dixit and colleagues show that the absence or presence of NPC1 and NPC2 has no effect on intestinal cholesterol absorption in the mouse. Thus neither protein fills the gap in our knowledge of intra-enterocyte cholesterol transport. Furthermore, the NPC1/NPC2 pathway would not be a good target for limiting the uptake of dietary cholesterol.
Rare gas collisions with molten metal surfaces
Authors: Hayes W. W. , Manson J. R.
Published: October 2007

Newly available experimental data for the scattering of argon, neon, and xenon atoms from molten gallium, indium, and bismuth surfaces are compared to calculations with classical scattering theory. The results of the theory are in reasonable agreement with observed energy-resolved spectra taken at fixed angles, with in-plane angular distributions, and with the first available out-of-plane angular distribution spectra for these systems. For all three of the rare gases, scattering from liquid Ga required the use of an effective surface mass equal to 1.65 times the mass of a single Ga atom. The need for a larger effective mass has been noted previously for Ar∕Ga scattering and is indicative of collective effects in the liquid Ga. Comparisons with data taken at low incident energies enable estimates of the physisorption well depth in the interaction potentials for many of the gas-metal combinations.
Modeling of plane Couette flow. II. On the spreading of a turbulent spot
Authors: Lagha Maher
Published: October 2007

In this paper, we study the spreading mechanism of turbulent spots in plane Couette flow, where fluid is sheared between two parallel plates moving in opposite directions. The analysis of the coherent structures on the border between the laminar and turbulent regions reveals the existence of many vortices with wall-normal axes occupying the full gap between the plates. The streamwise component of the velocity field of these vortices is the streaks. Due to their self-advection, these vortices move parallel to the plates. During their motions, they carry the other perturbation components such as the streamwise and spanwise vortices.
Hyper-Rayleigh and hyper-Raman scatterings with intermediate and two-photon resonances
Authors: Leng Weinan , Kelley Anne Myers
Published: October 2007

The normally weak process of hyper-Raman scattering can be greatly enhanced when the excitation is two photon resonant with an electronic transition that is both one and two photon allowed. It might be expected to be further enhanced when a one-photon allowed transition provides an intermediate state resonance in the two-photon excitation step. The theory of this triply resonant process is developed for organic nonlinear chromophores. Experimental results are obtained for one donor-acceptor substituted push-pull chromophore in which the energy of the strongly allowed lowest-lying one-photon state may be tuned by varying the solvent without substantially affecting the two-photon resonant transition. Surprisingly, bringing the one-photon allowed state into resonance does not significantly increase the hyper-Rayleigh or hyper-Raman hyperpolarizabilities. Analysis of the resonance Raman, hyper-Rayleigh, and hyper-Raman profiles suggests that the triply resonant path does not make the dominant contribution to the hyperpolarizability in this system.
Application of principal component analysis in protein unfolding: An all-atom molecular dynamics simulation study
Authors: Das Atanu , Mukhopadhyay Chaitali
Published: October 2007

We have performed molecular dynamics (MD) simulation of the thermal denaturation of one protein and one peptide—ubiquitin and melittin. To identify the correlation in dynamics among various secondary structural fragments and also the individual contribution of different residues towards thermal unfolding, principal component analysis method was applied in order to give a new insight to protein dynamics by analyzing the contribution of coefficients of principal components. The cross-correlation matrix obtained from MD simulation trajectory provided important information regarding the anisotropy of backbone dynamics that leads to unfolding. Unfolding of ubiquitin was found to be a three-state process, while that of melittin, though smaller and mostly helical, is more complicated.
Light emission during shock wave focusing in air and argon
Authors: Eliasson Veronica , Tillmark Nils , Szeri Andrew J. , Apazidis Nicholas
Published: October 2007

The light emission from a converging shock wave was investigated experimentally. Results show that the shape of the shock wave close to the center of convergence has a large influence on the amount of emitted light. It was found that a symmetrical polygonal shock front produced more light than an asymmetrical shape. The light emission appears as the shock wave collapses. The full width at half maximum of the light pulse is about 200ns for all geometrical shapes. It was also found that argon as a test gas produces more light than air. Numerical simulations showed good agreement with experimental results regarding the shape of the shock and the flow field behind the shock. The temperature field from the numerical simulations was investigated and shows that the triple points behind the shock front are hot spots that increase the temperature at the center as they arrive there.
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-algebraic approach to the Bose-Hubbard model
Authors: Adams Stefan , Dorlas Tony
Published: October 2007

We give a new derivation of the variational formula for the pressure of the long-range-hopping Bose-Hubbard model, which was first proven by Bru and Dorlas [J. Stat. Phys. 113, 177 (2003)]. The proof is analogous to that of a theorem on noncommutative large deviations introduced by Petz et al. [Commun. Math. Phys. 121, 271 (1989)] and could similarly be extended to more general Bose systems of mean-field type. We apply this formalism to prove Bose-Einstein condensation for the case of small coupling.
Conceptual aspects of line tensions
Authors: Schimmele L. , Napiórkowski M. , Dietrich S.
Published: October 2007

We analyze two representative systems containing a three-phase-contact line: a liquid lens at a fluid-fluid interface and a liquid drop in contact with a gas phase residing on a solid substrate. In addition we study a system containing a planar liquid-gas interface in contact with a solid substrate. We discuss to which extent the decomposition of the grand canonical free energy of such systems into volume, surface, and line contributions is unique in spite of the freedom one has in positioning the Gibbs dividing interfaces. Curvatures of interfaces are taken into account. In the case of a lens it is found that the line tension is independent of arbitrary choices of the Gibbs dividing interfaces. In the case of a drop, however, one arrives at two different possible definitions of the line tension. One of them corresponds seamlessly to that applicable to the lens. The line tension defined this way turns out to be independent of choices of the Gibbs dividing interfaces. In the case of the second definition, however, the line tension does depend on the choice of the Gibbs dividing interfaces. We also provide form invariant equations for the equilibrium contact angles which properly transform under notional shifts of dividing interfaces which change the description of the system but leave the density configurations unchanged. It is shown that in order to accomplish this form invariance, additional stiffness coefficients attributed to the contact line must be introduced. The choice of the dividing interfaces influences the actual values of the stiffness coefficients. We show how these coefficients transform as a function of the relative displacements of the dividing interfaces. Our formulation provides a clearly defined scheme to determine line properties from measured dependences of the contact angles on lens or drop volumes. This scheme implies relations different from the modified Neumann or Young equations, which currently are the basis for extracting line tensions from experimental data. These relations show that the experiments do not render the line tension alone but a combination of the line tension, the Tolman length, and the stiffness coefficients of the line. In contrast to previous approaches our scheme works consistently for any choice of the dividing interfaces. It further allows us to compare results obtained by different experimental or theoretical methods, based on different conventions of choosing the dividing interfaces.
Interaction of atomic hydrogen with the β-SiC(100) 3×2 surface and subsurface
Authors: D’angelo M. , Enriquez H. , Rodriguez N. , Aristov V. Yu. , Soukiassian P. , Tejeda A. , Michel E. G. , Pedio M. , Ottaviani C. , Perfetti P.
Published: October 2007

We investigate clean and atomic hydrogen exposed β-SiC(100) 3×2 surfaces by synchrotron radiation-based Si 2p core-level photoemission spectroscopy. The clean 3×2 surface reconstruction exhibits three surface and subsurface components. Upon hydrogen exposures, those surface and subsurface components are shifted to lower binding energies by large values, indicating significant charge transfer to the surface and subsurface regions, in excellent agreement with the recently discovered H-induced β-SiC(100) 3×2 surface metallization. In addition, the interaction of hydrogen results in a large reactive component at Si 2p supporting an asymmetric charge transfer in the third plane below the surface, in agreement with previous experimental investigations. However, the results are inconsistent with recent ab initio theoretical “frozen” calculations predicting H atom to be in a bridge-bond position.
Growth condition dependence of spin-polarized electroluminescence in Fe∕MgO∕light-emitting diodes
Authors: Manago Takashi , Sinsarp Asawin , Akinaga Hiro
Published: October 2007

We compared the electroluminescence (EL) polarization of two Fe∕MgO∕light-emitting-diode (LED) structures grown at different substrate temperatures for MgO growth: room temperature and 400°C. Two spin-LED wafers were prepared on molecular beam epitaxy grown LEDs by e-beam evaporation: one was LED∕MgO (RT)∕Fe (RT)∕Au cap (RT), and the other was LED∕MgO (400°C)∕Fe (150°C)∕Au cap (90°C). Spin-polarized EL was clearly observed in the latter sample, while the EL polarization was hardly observed in the former sample. The reasons for the near absence of EL polarization in the former sample are considered to be the degradation of the tunneling junction resulting from the crystallinity and the As-rich surface of the LED.
Energy loss and straggling of MeV ions through biological samples
Authors: Ma Lei , Wang Yugang , Xue Jianming , Chen Qizhong , Zhang Weiming , Zhang Yanwen
Published: October 2007

Energy loss and energy straggling of energetic ions through natural dehydrated biological samples were investigated using transmission technique. Biological samples (onion membrane, egg coat, and tomato coat) with different mass thickness were studied, together with Mylar for comparison. The energy loss and energy straggling of MeV H and He ions after penetrating the biological and Mylar samples were measured. The experimental results show that the average energy losses of MeV ions through the biological samples are consistent with SRIM predictions; however, large deviation in energy straggling is observed between the measured results and the SRIM predictions. Taking into account inhomogeneity in mass density and structure of the biological sample, an energy straggling formula is suggested, and the experimental energy straggling values are well predicted by the proposed formula.
Influence of proximity effects in electron-beam lithography on the optical properties of planar photonic-crystal waveguides
Authors: Wüest R. , Robin F. , Strasser P. , Jäckel H. , Erni D.
Published: October 2007

To measure the influence of proximity effects in electron-beam lithography on the optical properties of planar photonic crystal (PPC) waveguides we propose a PPC structure called the “PECmeter.” The PECmeter consists of nearly identical PPC waveguides which only differ in the number of rows of holes along the waveguide. The difference in the number of rows does not influence the modal properties directly but changes the diameter of the holes neighboring the waveguide through the proximity effect. The operation principle of the PECmeter is demonstrated using energy-intensity simulations of a W3 waveguide (three missing rows of holes) mini stop band. The principle is confirmed experimentally with structures fabricated in the InP-based material system and measured by the end-fire transmission technique. The results clearly show that the application of proximity-effect correction (PEC) is crucial for the fabrication of PPC waveguides. We demonstrate that when using the midpoint-equalization PEC method a near-to-perfect correction with sub-nm hole-radius uniformity can be achieved. We show the PECmeter to be sensitive enough to detect hole-radius changes as small as ΔR=0.4 nm.
Compositional dependence of ultrasonic velocities in glasses
Authors: Annapurna K. , Tarafder Anal , Phani K. K.
Published: October 2007

This paper analyzes the variation of ultrasonic wave velocities in glasses with change in compositions based on the variation of Poisson’s ratio (ν) and fractal bond connectivity (d) of these glasses. It shows that for the same Poisson’s ratio value, the ratio of ultrasonic shear wave velocity to longitudinal velocity is independent of the composition and varies linearly with the longitudinal velocity. The suggested linear variation of velocity ratio with longitudinal velocity shows a good agreement with the experimental data obtained from the previously published studies.