Out of Plane Distortions of the Heme b of Escherichia coli Succinate Dehydrogenase

The role of the heme b in Escherichia coli succinate dehydrogenase is highly ambiguous and its role in catalysis is questionable. To examine whether heme reduction is an essential step of the catalytic mechanism, we generated a series of site-directed mutations around the heme binding pocket, creating a library of variants with a stepwise decrease in the midpoint potential of the heme from the wild-type value of +20 mV down to −80 mV. This difference in midpoint potential is enough to alter the reactivity of the heme towards succinate and thus its redox state under turnover conditions. Our results show both the steady state succinate oxidase and fumarate reductase catalytic activity of the enzyme are not a function of the redox potential of the heme. As well, lower heme potential did not cause an increase in the rate of superoxide production both in vitro and in vivo. The electron paramagnetic resonance (EPR) spectrum of the heme in the wild-type enzyme is a combination of two distinct signals. We link EPR spectra to structure, showing that one of the signals likely arises from an out-of-plane distortion of the heme, a saddled conformation, while the second signal originates from a more planar orientation of the porphyrin ring

Zidovudine and dideoxynucleosides deplete wild-type mitochondrial DNA levels and increase deleted mitochondrial DNA levels in cultured Kearns-Sayre syndrome fibroblasts

AbstractKearns-Sayre syndrome is the most commonly diagnosed mitochondrial cytopathy and produces severe neuromuscular symptoms. The most frequent cause is a mitochondrial DNA deletion that removes a 4977-base pair segment of DNA that includes several genes encoding for respiratory chain subunits. Treatment of AIDS patients with nucleoside analogs has been reported to cause mtDNA depletion and myopathies. Here, we report that azidothymidine, dideoxyguanosine, and dideoxycytidine cause a depletion of wild-type mtDNA while increasing the levels of deleted mitochondria DNA in Kearns-Sayre syndrome fibroblasts. The result of these effects is a large increase in the relative amounts of ΔmtDNA in comparison to wild type mtDNA. We found that Kearns-Sayre syndrome fibroblasts are a mixed population of cells with deleted mtDNA comprising from 0 to over 20% of the total mtDNA in individual cells. Treatment of cloned cell lines with dideoxycytidine did not result in increased levels of ΔmtDNA. The results suggest that nucleoside analogs may act to increase the average ΔmtDNA levels in a mixed population of cells by preferentially inhibiting the proliferation of cells with little or no ΔmtDNA. This raises the possibility that modulation of deleted mtDNA levels may occur by similar mechanisms in vivo, in response to the influence of exogenous agents

Electrochemical evidence that pyranopterin redox chemistry controls the catalysis of YedY, a mononuclear Mo enzyme

A long-standing contradiction in the field of mononuclear Mo enzyme research is that small-molecule chemistry on active-site mimic compounds predicts ligand participation in the electron transfer reactions, but biochemical measurements only suggest metal-centered catalytic electron transfer. With the simultaneous measurement of substrate turnover and reversible electron transfer that is provided by Fourier-transformed alternating-current voltammetry, we show that Escherichia coli YedY is a mononuclear Mo enzyme that reconciles this conflict. In YedY, addition of three protons and three electrons to the well-characterized "as-isolated" Mo(V) oxidation state is needed to initiate the catalytic reduction of either dimethyl sulfoxide or trimethylamine N-oxide. Based on comparison with earlier studies and our UV-vis redox titration data, we assign the reversible one-proton and one-electron reduction process centered around +174 mV vs. standard hydrogen electrode at pH 7 to a Mo(V)-to-Mo(IV) conversion but ascribe the two-proton and two-electron transition occurring at negative potential to the organic pyranopterin ligand system. We predict that a dihydro-to-tetrahydro transition is needed to generate the catalytically active state of the enzyme. This is a previously unidentified mechanism, suggested by the structural simplicity of YedY, a protein in which Mo is the only metal site

Ultrasound guided drainage of an esophageal duplication cyst in a newborn in respiratory distress

AbstractNewborns with chest masses may present with respiratory distress in the perinatal period. We present the case of a term male infant with a cystic right upper chest mass born in respiratory distress at 39 4/7 weeks gestation who underwent ultrasound guided percutaneous drainage of the mass. The patient responded well to the percutaneous drainage and two days later the mass was surgically excised. Final pathology revealed an esophageal duplication cyst. This report describes a unique management of a patient with a congenital cystic chest mass presenting in respiratory distress

Rule violation errors are associated with right lateral prefrontal cortex atrophy in neurodegenerative disease

Good cognitive performance requires adherence to rules specific to the task at hand. Patients with neurological disease often make rule violation errors, but the anatomical basis for rule violation during cognitive testing remains debated. The current study examined the neuroanatomical correlates of rule violation (RV) errors made on tests of executive functioning in 166 subjects diagnosed with neurodegenerative disease or as neurologically healthy. Specifically, RV errors were voxel-wisely correlated with gray matter volume derived from high-definition MR images using voxel-based morphometry implemented in SPM2. Latent variable analysis showed that rule violation errors tapped a unitary construct separate from repetition errors. This analysis was used to generate factor scores to represent what is common among rule violation errors across tests. The extracted rule violation factor scores correlated with tissue loss in the lateral middle and inferior frontal gyri and the caudate nucleus bilaterally. When a more stringent control for global cognitive functioning was applied using Mini Mental State Exam scores, only the correlations with the right lateral prefrontal cortex remained significant. These data underscore the importance of right lateral prefrontal cortex in behavioral monitoring and highlight the potential of rule violation error assessment for identifying patients with damage to this region

Joint Assessment of Structural, Perfusion, and Diffusion MRI in Alzheimer's Disease and Frontotemporal Dementia

Most MRI studies of Alzheimer's disease (AD) and frontotemporal dementia (FTD) have assessed structural, perfusion and diffusion abnormalities separately while ignoring the relationships across imaging modalities. This paper aimed to assess brain gray (GM) and white matter (WM) abnormalities jointly to elucidate differences in abnormal MRI patterns between the diseases. Twenty AD, 20 FTD patients, and 21 healthy control subjects were imaged using a 4 Tesla MRI. GM loss and GM hypoperfusion were measured using high-resolution T1 and arterial spin labeling MRI (ASL-MRI). WM degradation was measured with diffusion tensor imaging (DTI). Using a new analytical approach, the study found greater WM degenerations in FTD than AD at mild abnormality levels. Furthermore, the GM loss and WM degeneration exceeded the reduced perfusion in FTD whereas, in AD, structural and functional damages were similar. Joint assessments of multimodal MRI have potential value to provide new imaging markers for improved differential diagnoses between FTD and AD

Concordance and Discordance Between Brain Perfusion and Atrophy in Frontotemporal Dementia

The aim of this study was to determine if a dissociation between reduced cerebral perfusion and gray matter (GM) atrophy exists in frontotemporal dementia (FTD). The study included 28 patients with FTD and 29 cognitive normal (CN) subjects. All subjects had MRI at 1.5 T, including T1-weighted structural and arterial spin labeling (ASL) perfusion imaging. Non-parametric concordance/discordance tests revealed that GM atrophy without hypoperfusion occurs in the premotor cortex in FTD whereas concordant GM atrophy and hypoperfusion changes are found in the right prefrontal cortex and bilateral medial frontal lobe. The results suggest that damage of brain function in FTD, assessed by ASL perfusion, can vary regionally despite widespread atrophy. Detection of discordance between brain perfusion and structure in FTD might aid diagnosis and staging of the disease

The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey

The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median z=0.52), 102,100 new quasar spectra (median z=2.32), and 90,897 new stellar spectra, along with the data presented in previous data releases. These spectra were obtained with the new BOSS spectrograph and were taken between 2009 December and 2011 July. In addition, the stellar parameters pipeline, which determines radial velocities, surface temperatures, surface gravities, and metallicities of stars, has been updated and refined with improvements in temperature estimates for stars with T_eff<5000 K and in metallicity estimates for stars with [Fe/H]>-0.5. DR9 includes new stellar parameters for all stars presented in DR8, including stars from SDSS-I and II, as well as those observed as part of the SDSS-III Sloan Extension for Galactic Understanding and Exploration-2 (SEGUE-2). The astrometry error introduced in the DR8 imaging catalogs has been corrected in the DR9 data products. The next data release for SDSS-III will be in Summer 2013, which will present the first data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) along with another year of data from BOSS, followed by the final SDSS-III data release in December 2014.Comment: 9 figures; 2 tables. Submitted to ApJS. DR9 is available at http://www.sdss3.org/dr