The mechanism of assembly and cofactor insertion into Rhodobacter capsulatus xanthine dehydrogenase

Rhodobacter capsulatus xanthine dehydrogenase (XDH) is a molybdo-flavoprotein that is highly homologous to the homodimeric mammalian xanthine oxidoreductase. However, the bacterial enzyme has an (alphabeta)(2) heterotetrameric structure, and the cofactors were identified to be located on two different polypeptides. We have analyzed the mechanism of cofactor insertion and subunit assembly of R. capsulatus XDH, using engineered subunits with appropriate substitutions in the interfaces. In an (alphabeta) heterodimeric XDH containing the XdhA and XdhB subunits, the molybdenum cofactor (Moco) was shown to be absent, indicating that dimerization of the (alphabeta) subunits has to precede Moco insertion. In an (alphabeta)(2) XDH heterotetramer variant, including only one active Moco-center, the active (alphabeta) site of the chimeric enzyme was shown to be fully active, revealing that the two subunits act independent without cooperativity. Amino acid substitutions at two cysteine residues coordinating FeSI of the two [2Fe-2S] clusters of the enzyme demonstrate that an incomplete assembly of FeSI impairs the formation of the XDH (alphabeta)(2) heterotetramer and, thus, insertion of Moco into the enzyme. The results reveal that the insertion of the different redox centers into R. capsulatus XDH takes place sequentially. Dimerization of two (alphabeta) dimers is necessary for insertion of sulfurated Moco into apo-XDH, the last step of XDH maturation.     

Forebrain neurons that project to the gustatory parabrachial nucleus in rat lack glutamic acid decarboxylase

Evidence suggests that GABA might mediate the inhibitory influence of centrifugal inputs on taste-evoked responses in the parabrachial nucleus (PBN). Previous studies show that activation of the gustatory cortex (GC), bed nucleus of the stria terminalis (BNST), central nucleus of the amygdala (CeA), and lateral hypothalamus (LH) inhibits PBN taste responses, GABAergic neurons are present in these forebrain regions, and GABA reduces the input resistance of PBN neurons. The present study investigated the expression of glutamic acid decarboxylase immunoreactivity (GAD_67 ir) in GC, BNST, CeA, and LH neurons that project to the PBN in rats. After anesthesia (50 mg/kg ip Nembutal), injections of the retrograde tracer Fluorogold (FG) were made in the physiologically defined gustatory PBN. Brain tissue containing the above forebrain structures was processed and examined for FG and GAD_67 ir. Similar to previous studies, each forebrain site contained retrogradely labeled neurons. Our results suggest further that the major source of input to the PBN taste region is the CeA (608 total cells) followed by GC (257 cells), LH (106 cells), and BNST (92 cells). This suggests a differential contribution to centrifugal control of PBN taste processing. We further show that despite the presence of GAD_67 neurons in each forebrain area, colocalization was extremely rare, occurring only in 3 out of 1,063 FG-labeled cells. If we assume that the influence of centrifugal input is mediated by direct projections to the gustatory region of the PBN, then GABAergic forebrain neurons apparently are not part of this descending pathway.     

Design, synthesis, and evaluation of novelly substituted benzimidazole compounds as angiotensin II receptor antagonists

5-Nitrobenzimidazole derivatives with varying substituents at 2-position have been designed, synthesized, and evaluated for angiotensin II antagonistic activity. A drug-receptor interaction model has been proposed.     

Nitric Oxide: A Ubiquitous Signal Molecule for Enhancing Plant Tolerance to Salinity Stress and Their Molecular Mechanisms

Journal of Plant Growth Regulation - Salinity is a major constraint of agricultural productivity globally and is recognized to be severely elevated by alterations in the climatic conditions. High...     

A unique iron-sulfur cluster is crucial for oxygen tolerance of a [NiFe]-hydrogenase

Hydrogenases are essential for H(2) cycling in microbial metabolism and serve as valuable blueprints for H(2)-based biotechnological applications. However, most hydrogenases are extremely oxygen sensitive and prone to inactivation by even traces of O(2). The O(2)-tolerant membrane-bound [NiFe]-hydrogenase of Ralstonia eutropha H16 is one of the few examples that can perform H(2) uptake in the presence of ambient O(2). Here we show that O(2) tolerance is crucially related to a modification of the internal electron-transfer chain. The iron-sulfur cluster proximal to the active site is surrounded by six instead of four conserved coordinating cysteines. Removal of the two additional cysteines alters the electronic structure of the proximal iron-sulfur cluster and renders the catalytic activity sensitive to O(2) as shown by physiological, biochemical, spectroscopic and electrochemical studies. The data indicate that the mechanism of O(2) tolerance relies on the reductive removal of oxygenic species guided by the unique architecture of the electron relay rather than a restricted access of O(2) to the active site.     

Effect of Endoxylanase and Iron Oxide Nanoparticles on Performance and Histopathological Features in Broilers

Biological Trace Element Research - Endoxylanase enzyme is used as poultry feed additive to degrade anti-nutritional factors like non-starch polysaccharides. Moreover, iron is one of the most...     

Catheter Ablation in Patients with Electrical Storm in Early Post Infarction Period (6 Weeks): A Single Centre Experience

Background

Electrical storm (ES) due to drug refractory ventricular tachycardia (VT) occurring within first few weeks of acute myocardial infarction (MI) has poor prognosis. Catheter ablation has been proposed for treating VT occurring late after MI, but there is limited data on catheter ablation in VT within first few weeks of MI.

Methods and Results

Five patients (4 males, mean age 54.2±12.11 years) between June 2008 to July 2012, referred for VT presenting as ES refractory to antiarrhythmic drugs in the early post infarction period (six weeks following MI) despite revascularization. Three patients had anterior wall MI and two inferior wall MI with left ventricular ejection fraction ranging from 26 to 35%.All underwent catheter ablation within 48 hours of being in VT except one who presented late. Clinical VT was induced in all five patients. Total number of VTs induced were 11 (2.2±1.09 per patient). Two patients needed epicardial ablation via pericardial puncture. Though acute success was 100%, one patient had recurrence of clinical VT the next day of procedure.One patient succumbed to sepsis with multiple organ failure. The remaining four patients are doing well without further clinical recurrence of VT over a period of 3.7 years of follow-up.

Conclusion

Catheter ablation can be a useful adjunctive therapy for patients with recurrent VT in the early post infarction period. This procedure appears to be safe with acceptable success rate.