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Methionine sulfoxide reductase A: Structure, function and role in ocular pathology

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World Journal of Biological Chemistry 2011年第8期2卷 184-192页

作者： parameswaran g sreekumar David R Hinton Ram Kannan Arnold and Mabel Beckman Macular Research Center Doheny Eye Institute Department of Pathology Keck School of Medicine of the University of Southern California

Methionine is a highly susceptible amino acid that can be oxidized to S and R diastereomeric forms of methionine sulfoxide by many of the reactive oxygen species generated in biological systems. Methionine sulfoxide reductases (Msrs) are thioredoxin-linked enzymes involved in the enzymatic conversion of methionine sulfoxide to methionine. Although MsrA and MsrB have the same function of methionine reduction, they differ in substrate specifi city, active site composition, subcellular localization, and evolution. MsrA has been localized in different ocular regions and is abundantly expressed in the retina and in retinal pigment epithelial (RPE) cells. MsrA protects cells from oxidative stress. Overexpression of MsrA increases resistance to cell death, while silencing or knocking down MsrA decreases cell survival; events that are mediated by mitochondria. MsrA participates in protein-protein interaction with several other cellular proteins. The interaction of MsrAwith α-crystallins is of utmost importance given the known functions of the latter in protein folding, neuroprotection, and cell survival. Oxidation of methionine residues in α-crystallins results in loss of chaperone function and possibly its antiapoptotic properties. Recent work from our laboratory has shown that MsrA is co-localized with αA and αB crystallins in the retinal samples of patients with age-related macular degen- eration. We have also found that chemically induced hypoxia regulates the expression of MsrA and MsrB2 in human RPE cells. Thus, MsrA is a critical enzyme that participates in cell and tissue protection, and its interaction with other proteins/growth factors may provide a target for therapeutic strategies to prevent degenerative diseases.

关键词： Methionine sulfoxide reductases Hypoxia Protein interaction α crystallins Neuroprotection

Contribution from normal and starburst galaxies to the extragalactic gamma-ray background (EgRB)

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Chinese Journal of Astronomy and Astrophysics 2009年第5期9卷 509-519页

作者： Debbijoy Bhattacharya parameswaran sreekumar Department of Physics Indian Institute of Science Space Astronomy & Instrumentation Division ISRO Satellite Centre

The extragalactic diffuse emission at γ-ray energies has interesting cosmological implications since these photons suffer little or no attenuation during their propagation from the site of origin. The emission could originate from either truly diffuse processes or from unresolved point sources such as AgNs, normal galaxies and starburst galaxies. Here, we examine the unresolved point source origin of the extragalactic γ-ray background emission from normal galaxies and starburst galaxies. γ-ray emission from normal galaxies is primarily coming from cosmic-ray interactions with interstellar matter and radiation （-90%） along with a small contribution from discrete point sources （-10%）. Starburst galaxies are expected to have enhanced supernovae activity which leads to higher cosmic-ray densities, making starburst galaxies sufficiently luminous atγ-ray energies to be detected by the current γ-ray mission （Fermi gamma-ray Space Telescope）.

关键词： galaxy general -- galaxies luminosity function -- galaxies starburst -- gamma-rays observations

Contribution from unresolved discrete sources to the extragalactic gamma-ray background(EgRB)

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Research in Astronomy and Astrophysics 2009年第11期9卷 1205-1214页

作者： Debbijoy Bhattacharya parameswaran sreekumar Reshmi Mukherjee Department of Physics Indian Institute of Science Space Astronomy & Instrumentation Division ISRO Satellite Centre Barnard College Columbia University

The origin of the extragalactic gamma-ray background （EgRB） is still an open question, even nearly forty years after its discovery. The emission could originate either from truly diffuse processes or from unresolved point sources. Although the majority of the 271 point sources detected by EgRET （Energetic gamma Ray Experiment Telescope） are unidentified, of the identified sources, blazars are the dominant candidates. Therefore, unresolved blazars may be considered the main contributor to the EgRB, and many studies have been carried out to understand their distribution, evolution and contribution to the EgRB. Considering that γ-ray emission comes mostly from jets of blazars and that the jet emission decreases rapidly with increasing jet to line-of-sight angle, it is not surprising that EgRET was not able to detect many large inclination angle active galactic nuclei （AgNs）. Though Fermi could only detect a few large inclination angle AgNs during the first three months of its survey, it is expected to detect many such sources in the near future. Since non-blazar AgNs are expected to have higher density as compared to blazars, these could also contribute significantly to the EgRB. In this paper, we discuss contributions from unresolved discrete sources including normal galaxies, starburst galaxies, blazars and off-axis AgNs to the EgRB.

关键词： galaxies active -- galaxies jets -- gamma-rays observations

Does black hole spin play a key role in the FSRQ/BL Lac dichotomy?

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Research in Astronomy and Astrophysics 2016年第4期16卷 7-14页

作者： Debbijoy Bhattacharya parameswaran sreekumar Banibrata Mukhopadhyay Ishan Tomar Manipal Centre for Natural Sciences Manipal UniversityManipal 576104India Indian Institute of Astrophysics Bangalore 560034India Astronomy and Astrophysics Programme Department of PhysicsIndian Institute of ScienceBangalore 560012India Space Astronomy group ISRO Satellite CentreKarthik NagarBangalore 560037India

Blazars are characterized by large intensity and spectral variations across the electromagnetic spectrum It is believed that jets emerging from them are almost aligned with the line-of-sight. The major- ity of identified extragalactic sources in γ-ray catalogs of EgRET and Fermi are blazars. Observationally, blazars can be divided into two classes： fiat spectrum radio quasars （FSRQs） and BL Lacs. BL Lacs usually exhibit lower γ-ray luminosity and harder power law spectra at γ-ray energies than FSRQs. We attempt to explain the high energy properties of FSRQs and BL Lacs from Fermi γ-ray space telescope observations. It was argued previously that the difference in accretion rates is mainly responsible for the large mismatch in observed luminosity in ＂7-ray. However, when intrinsic luminosities are derived by correcting for beaming effects, this difference in 7-ray luminosity between the two classes is significantly reduced. In order to ex- plain this difference in intrinsic luminosities, we propose that spin plays an important role in the luminosity distribution dichotomy of BL Lacs and FSRQs. As the outflow power of a blazar increases with increasing spin of a central black hole, we suggest that the spin plays a crucial role in making BL Lac sources low luminous and slow rotators compared to FSRQ sources.

关键词： BL Lacertae objects: general -- quasars: general -- galaxies: jets -- black hole physics --relativistic processes -- gravitation

Lipid enhancement in microalgae by temporal phase separation:Use of indigenous sources of nutrients

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Chinese Journal of Chemical Engineering 2018年第1期26卷 175-182页

作者： Nidhin sreekumar Ajit Haridas g.S.godwin N.Selvaraju National Institute of Technology(NITC) CalicutIndia National Institute for Interdisciplinary Science and Technology(NIIST) Council of Scientific&Industrial Research(CSIR)ThiruvananthapuramIndia

Microalgae have been recommended as superior candidate for fuel production because of their advantages of higher photosynthetic efficiency, biomass & lipid productivity, and faster growth rate as compared to other energy crops. To meet up all these criteria, we have developed a continuous outdoor micro-algal raceway pond reactor(RPR) and a lab scale indoor tubular photo bioreactor(PBR) for biofuel production. An attempt to utilise indigenous sources of nutrients to improve the economics also revealed that micro-algal culturing can also be used as a mode of nutrient removal and water treatment. The photosynthetic rate and lipid production were enhanced by arresting daytime cell division and promoting night-time cell division. A 50% lipid improvement was observed for the particular algal consortia. Microscopic studies revealed that temporal phase separation could be achieved by adjusting nutrient distribution pattern. To monitor temporal phase separation, it is required to know DNA multiplication model. Quantification of g DNA in RPR confirmed that cell division happens during the night which positively affects the photosynthetic efficiency and lipid productivity of microalgae.

关键词： Temporal phase separation Lipid enhancement Microalgae Biodiesel

On the line profile changes observed during the X2.2 class flare in the active region NOAA 11158

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Research in Astronomy and Astrophysics 2014年第2期14卷 207-220页

作者： Ankala Raja Bayanna Brajesh Kumar parameswaran Venkatakrishnan Shibu Kunchandy Mathew Belur Ravindra Savita Mathur Rafael A garcia Udaipur Solar Observatory Physical Research LaboratoryDewaliBadi RoadUdaipur 313 004India Indian Institute of Astrophysics II BlockKoramanglaBangalore 560034India Space Science Institute 4750 Walnut Street Suite#205BoulderCO 80301USA Laboratoire AIM CEA/DSM-CNRSUniversit'e Paris 7 DiderotIRFU/SApCentre de Saclay91191Gif-sur-YvetteFrance

The solar active region NOAA 11158 produced a series of flares during its passage through the solar disk. The first major flare （of class X2.2） of the current solar cycle occurred in this active region on 2011 February 15 around 01：50 UT. We have analyzed the Dopplergrams and magnetograms obtained by the Helioseismic and Magnetic Imager （HMI） instrument onboard Solar Dynamics Observatory to examine the photospheric velocity and magnetic field changes associated with this flare. The HMI instrument provides high-quality Doppler and magnetic maps of the solar disk with 0.5＂ spatial scale at a cadence of 45 s along with imaging spectroscopy. We have identified five locations of velocity transients in the active region during the flare. These transient velocity signals are located in and around the flare ribbons as observed by Hinode in the Ca II H wavelength and the footpoints of hard X-ray enhancement are in the energy range 12-25 keV from RHESSI. The changes in shape and width of two circular polarization states have been observed at the time of transients in three out of five locations. Forward modeling of the line profiles shows that the change in atmospheric parameters such as magnetic field strength, Doppler velocity and source function could explain the observed changes in the line profiles with respect to the pre-flare condition.

关键词： Sun: activity -- Sun: sunspot -- Sun: flares -- Sun: spectroscopy --Sun: velocity and magnetic fields

Effect of micro arc oxidation treatment on localized corrosion behaviour of AA7075 aluminum alloy in 3.5% NaCl solution

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Transactions of Nonferrous Metals Society of China 2012年第3期22卷 700-710页

作者： A.VENUgOPAL Rajiv PANDA Sushant MANWATKAR K.sreekumar L.RAMA KRISHNA g.SUNDARARAJAN Material Characterization Division Materials and Metallurgy GroupVikram Sarabhai Space CentreThiruvananthapuram-695022India International Advanced Research Centre for Powder Metallurgy and New Materials Hyderabad-500005India

Alumina coating was formed on AA7075 aluminum alloy by micro arc oxidation（MAO） method and its corrosion and stress corrosion cracking（SCC） behaviors were examined in 3.5%（mass fraction） NaCl *** impedance spectroscopy（EIS） was used to evaluate the degradation of the coating as a function of immersion time and was modeled with appropriate equivalent *** load stress corrosion cracking（SCC） results followed by post-test metallographic observations demonstrated the usefulness of MAO coating to avoid the premature failure of the alloy due to severe localized corrosion initiated by Cu-and Fe-rich intermetallic phases.

关键词： aluminum alloy micro arc oxidation impedance spectroscopy stress corrosion

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BAMO聚合物的合成与表征(英文)

含能材料 2006年第6期14卷 411-415页

作者： M.V.Maheshkumar M.J.Joseph K.sreekumar H-g.Ang Department of Applied Chemistry Cochin University of Science and Technology Cochin-682022 KeralaIndia Energetic Materials Research Centre Nanyang Technological University50 Nanyang Avenue Block N1-B4a-02Singapore 639 798

A new synthetic methodology has been developed for the synthesis of poly BAMO and poly BAMO-co-THF with controlled molecular weight and narrow molecular weight distribution. The synthesis of BCMO, the precursor of the BAMO monomer was accomplished using the reaction of Vilsmeir reagent with pentaerythritol. The BAMO monomer could be synthesized with an over all yield of 60% and polymerized using BF3·Et2O as the initiator and 1,4-butane diol as the co-initiator. Computational evaluation of the energy releasing properties of the poly BAMO derivatives was performed using gaussian algorithm. The theoretically calculated values agreed very well with the experimentally determined ones.

关键词：有机化学合成方法爆炸物 BAMO

In-Flight Formation of Nano-Crystalline Titanium Dioxide Powder in a Plasma Jet and Its Characterization

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Plasma Science and Technology 2010年第4期12卷 426-432页

作者： P. V. ANANTHAPADMANABHAN M. VIJAY T. K. THIYAgARAJAN K. P. sreekumar V. SELVARAJAN Jiaguo YU Shengwei LIU Laser & Plasma Technology Division Bhabha Atomic Research Centre Mumbai-400085 India Department of Physics Bharathiar University Coimbatore 641046 India State Key Laboratory of Advanced Technology for Material Synthesis and Processing Wuhan University of Technology Wuhan 430070 China

Nanocrystalline titanium dioxide powder was synthesized by in-flight oxidation of titanium dihydride （TiH2） powder in a thermal plasma jet. TiH2 powder was injected into the thermal plasma jet and allowed to react with oxygen injected downstream the jet. Characteriza- tion of the powder by various analytical tools indicated that the powder consisted of nano-sized titanium dioxide particles consisting predominantly of the anatase phase. It is suggested that the thermo-chemistry of the oxidation process contributes significantly to the formation of nano-sized titania. The large energy released during the oxidation process dissociates the TiO2 particles into TiO（g） and titanium vapour, which recombine downstream with oxygen and form nano particles of TiO2.

关键词： nanostructures titanium dioxide arc plasma synthesis reactive plasma pro- cessing surface properties