Electron spin resonance on a 2-dimensional electron gas in a single AlAs quantum well

Direct electron spin resonance (ESR) on a high mobility two dimensional electron gas in a single AlAs quantum well reveals an electronic $g$-factor of 1.991 at 9.35 GHz and 1.989 at 34 GHz with a minimum linewidth of 7 Gauss. The ESR amplitude and its temperature dependence suggest that the signal originates from the effective magnetic field caused by the spin orbit-interaction and a modulation of the electron wavevector caused by the microwave electric field. This contrasts markedly to conventional ESR that detects through the microwave magnetic field.Comment: 4 pages, 4 figure

A New Type of Electron Nuclear-Spin Interaction from Resistively Detected NMR in the Fractional Quantum Hall Effect Regime

Two dimensional electron gases in narrow GaAs quantum wells show huge longitudinal resistance (HLR) values at certain fractional filling factors. Applying an RF field with frequencies corresponding to the nuclear spin splittings of {69}Ga, {71}Ga and {75}As leads to a substantial decreases of the HLR establishing a novel type of resistively detected NMR. These resonances are split into four sub lines each. Neither the number of sub lines nor the size of the splitting can be explained by established interaction mechanisms.Comment: 4 pages, 3 figure

Phosphorylation of Glutamine Synthetase on Threonine 301 Contributes to Its Inactivation During Epilepsy

The astrocyte-specific enzyme glutamine synthetase (GS), which catalyzes the amidation of glutamate to glutamine, plays an essential role in supporting neurotransmission and in limiting NH4+ toxicity. Accordingly, deficits in GS activity contribute to epilepsy and neurodegeneration. Despite its central role in brain physiology, the mechanisms that regulate GS activity are poorly defined. Here, we demonstrate that GS is directly phosphorylated on threonine residue 301 (T301) within the enzyme’s active site by cAMP-dependent protein kinase (PKA). Phosphorylation of T301 leads to a dramatic decrease in glutamine synthesis. Enhanced T301 phosphorylation was evident in a mouse model of epilepsy, which may contribute to the decreased GS activity seen during this trauma. Thus, our results highlight a novel molecular mechanism that determines GS activity under both normal and pathological conditions.</p

The effects of nitroxyl (HNO) on soluble guanylate cyclase activity: interactions at ferrous heme and cysteine thiols

It has been previously proposed that nitric oxide (NO) is the only biologically relevant nitrogen oxide capable of activating the enzyme soluble guanylate cyclase (sGC). However, recent reports implicate HNO as another possible activator of sGC. Herein, we examine the affect of HNO donors on the activity of purified bovine lung sGC and find that, indeed, HNO is capable of activating this enzyme. Like NO, HNO activation appears to occur via interaction with the regulatory ferrous heme on sGC. Somewhat unexpectedly, HNO does not activate the ferric form of the enzyme. Finally, HNO-mediated cysteine thiol modification appears to also affect enzyme activity leading to inhibition. Thus, sGC activity can be regulated by HNO via interactions at both the regulatory heme and cysteine thiols

Development of a heme protein structure–electrochemical function database

Proteins containing heme, iron(protoporphyrin IX) and its variants, continue to be one of the most-studied classes of biomolecules due to their diverse range of biological functions. The literature is abundant with reports of structural and functional characterization of individual heme proteins which demonstrate that heme protein reduction potential values, Em, span the range from –550 mV to +450 mV versus SHE. In order to unite these data for the purposes of global analysis, a new web-based resource of heme protein structure–function relationships is presented: the Heme Protein Database (HPD). This database is the first of its kind to combine heme protein structural classifications including protein fold, heme type and heme axial ligands, with heme protein reduction potential values in a web-searchable format. The HPD is located at http://heme.chem.columbia.edu/heme.php. The data illustrate that heme protein Em values are modulated over a 300 mV range by the type of global protein fold, a 600 mV range by the type of porphyrin and an 800 mV range by the axial ligands. Thus, the 1 V range observed in heme protein reduction potential values in biological systems arises from subtle combinations of these various factors

Recipient and donor thrombophilia and the risk of portal venous thrombosis and hepatic artery thrombosis in liver recipients

<p>Abstract</p> <p>Background</p> <p>Vascular complications, such as HAT, are an important cause of graft loss and recipient mortality. We aimed to characterize post-transplant thrombotic events in a cohort of liver transplant recipients, and identify independent risk factors for these complications.</p> <p>Methods</p> <p>We conducted a thrombophilic study of 293 orthotopic liver transplants performed in the Digestive Surgery Department of the 12 de Octubre Hospital (Madrid, Spain) between January 2001 and December 2006.</p> <p>Results</p> <p>The most frequent post-transplant thrombotic events were HAT (9%) and PVT (1.7%). The one variable associated with post-transplant thrombotic event was a high fibrinogen level in the global cohort of liver transplantation. But toxicity as event post-OLT has been associated with post-transplant thrombotic event in the retrospective group and high fibrinogen level and low protein C levels were associated post-transplant thrombotic event in the prospective group. Liver disease relapse (HR 6.609, p < 0.001), high levels of FVIII (HR 1.008, p = 0.019)) and low levels of antithrombin (HR 0.946, p < 0.001) were associated with poor overall survival (OS).</p> <p>In conclusion, high fibrinogen and decreased protein C levels were associated with allograft thrombosis. Further studies are required in order to assess the clinical relevance of these parameters in prospective studies and to study the effect of anticoagulation prophylaxis in this group of risk.</p

New discoveries in the transmission biology of sleeping sickness parasites: applying the basics

The sleeping sickness parasite, Trypanosoma brucei, must differentiate in response to the changing environments that it encounters during its complex life cycle. One developmental form, the bloodstream stumpy stage, plays an important role in infection dynamics and transmission of the parasite. Recent advances have shed light on the molecular mechanisms by which these stumpy forms differentiate as they are transmitted from the mammalian host to the insect vector of sleeping sickness, tsetse flies. These molecular advances now provide improved experimental tools for the study of stumpy formation and function within the mammalian bloodstream. They also offer new routes to therapy via high-throughput screens for agents that accelerate parasite development. Here, we shall discuss the recent advances that have been made and the prospects for future research now available