DOCSLIB.ORG

Citric Acid Cycle

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Citric Acid Cycle CITRIC ACID CYCLE 1 Oxidation of Pyruvate under Aerobic Conditions: • The Oxidation of Pyruvate to Acetyl-CoA is the Irreversible Route from Glycolysis to the Citric Acid Cycle • Pyruvate, formed in the cytosol, is transported into the mitochondrion by a proton symporter. Inside the mitochondrion, pyruvate is oxidatively decarboxylated to acetyl-CoA by a multienzyme complex that is associated with the inner mitochondrial membrane, known as Pyruvate Dehydrogenase (PDH). 2 • PDH is an Irreversible Mitochondrial Enzyme. PDH Composed of Three Enzymes & Five Coenzymes. • PDH & all f the -ketoacid dehydrogenase complexes are enzyme complexes composed of multiple subunits of three different enzymes, E1, E2, and E3. 3 • E1 is an -ketoacid decarboxylase or Dehydrogenase contains thiamine pyrophosphate (TPP) which catalyzes the Decarboxylation of the carboxyl group of the -keto acid. • E2 is a transacylase containing lipoate; it transfers the acyl portion of the -keto acid from thiamine to CoASH. • E3 is dihydrolipoyl dehydrogenase, transfers the electrons from reduced lipoate to its tightly bound FAD molecule, thereby oxidizing lipoate back to its original disulfide form. 4 Pyruvate Dehydrogenase Complex 5 Coenzymes of Pyruvate Dehydrogenase Complex •Thiamin Pyrophosphate (TPP) in the PDH: • The acyl portion of the -keto acid is transferred by TPP on E1 to lipoate on E2. Then, E2 transfers the acyl group from lipoate to CoASH. • This process has reduced the lipoyl disulfide bond to sulfhydryl groups (dihydrolipoyl). 6 Lipoic acid & Transacylase Enzyme •Lipoate is attached to the transacylase enzyme (E2) through its carboxyl group & the terminal -NH2 of a lysine of the E2. •The oxidized lipoate disulfide form is reduced as it accepts the acyl group from TPP attached to E1. •Lipoic picks up the acyl fragment from thiamine and transfer it to the active site containing bound CoASH. 7 8 Coenzyme A (CoASH) • E2 transfers the acyl group from lipoate to CoASH with reduction of the lipoyl disulfide to sulfhydryl group (dihydrolipoyl). SH of mercaptoethylamine forms a thioester high energy bond with acetate to form AcetylCoA. 9 FAD (Flavine adenine dinucleotides) • Composed of Adenine dinucleotide + Ribitol +Isoalloxazine. • -SH gp of Dihydrolipoic acid is oxidized by FAD (prosthetic gp of E3) + • Nitrogens 1& 5 of the Isoalloxazine ring carry the 2 H in FADH2. 10 (5) NAD (Nicotinamide Adenine Dinucleotide) • FADH2 of E3 donates its 2 ele & H- to NAD. PDH is now ready for another catalytic cycle. 11 Regulation of Pyruvate Dehydrogenase complex (PDH) • 1) PDH kinase, phosphorylates PDH converting it to an inactive form. The PDH kinase is inhibited by ADP & Pyruvate. • 2) PDH phosphatase, removes the phosphate, activating PDH. • The phosphatase is activated by Ca2+. In heart, increased intramitochondrial Ca2+ during contraction activates the phosphatase, thereby increasing the amount of active, nonphosphorylated PDH. • 3) Pyruvate & CoASH, when are bound to PDH, the kinase activity is inhibited & PDH is active. 12 Pyruvate Dehydrogenase Regulated by Covalent Modification 13 4) Pyruvate Dehydrogenase Is Regulated by End-Product Inhibition & Covalent Modification. • Acetyl CoA & NADH, when these products bind to PDH, the kinase activity is stimulated, and the enzyme is phosphorylated to the inactive form & by dephosphorylation by a phosphatase that causes an increase in activity. 14 5) The kinase is activated by increases in the: • ATP]/[ADP], [acetylCoA]/[CoA], & [NADH]/[NAD+] ratios. • Thus, PDH is inhibited not only by a high-energy potential but also when fatty acids are being oxidized. 1. PDH kinase is, itself, inhibited by ADP & pyruvate. Thus, when activation of glycolysis increases pyruvate levels, PDH kinase is inhibited & PDH remains in an active, nonphosphorylated form. 2. Insulin may increase the amount of PDH complex. 15 • Arsenic Poisoning: it is caused by the presence of a large number of different Arsenious compounds that are effective metabolic inhibitors. Acute accidental or intentional arsenic poisoning requires 2- 2- high doses and involves Arsenate (AsO4 ) & arsenite (AsO ). 16 • Arsenite, is 10 times more toxic than arsenate, it binds to neighboring –SH groups, such as those in dihydrolipoate & in cysteine pairs (vicinal) found in - keto acid dehydrogenase complexes and in succinic dehydrogenase. • Arsenate weakly inhibits enzymatic reactions involving phosphate, including the enzyme glyceraldehydes 3-P dehydrogenase in glycolysis (see Chapter 2). • Thus both aerobic and anaerobic ATP production can be inhibited. The low doses of arsenic compounds found in water supplies are a major public health concern, but are associated with increased risk of cancer rather than direct toxicity. 17 CITRIC ACID CYCLE • The Citric Acid Cycle (CAC) also called Tricarboxylic acid cycle (TCA cycle), or the Krebs cycle plays several roles in metabolism. It is the final pathway where the oxidative metabolism of carbohydrates, amino acids & fatty acids converge, their carbon skeletons being converted to CO2 and H2O. 18 • The cycle occurs in the mitochondria in close proximity to the electron transport, to oxidize the reduced coenzymes produced by the cycle. • The TCA cycle is an aerobic pathway, because O2 is required as the final electron acceptor. • The CAC also participates in a number of important synthetic reactions e.g., heme. Some intermediates of TCA cycle can synthesized by some amino acids. 19 The Overall Pattern of the Citric Acid Cycle: 20 The CAC has 8 Steps that can be divided into TWO Phases: •- First Phase: Removal of 2 mole of CO2 (reaction 1 to 5). •- The 2nd Phase: Regeneration of Oxaloacetate (reaction 6 to 8). 21 Phase One: Removal of Two Molecules of CO2: • Reaction1: Citrate synthase (CS) condenses Oxaloacetate (OAA) with AcetylCoA to form Citrate, by an irreversible aldol condensation to generate a highly unstable Citroyl-CoA which hydrolyzes to yield Citrate. 22 • No Coenzymes Required • The reaction is highly exergonic & has been considered to be a site of regulation for the overall pathway. • Citrate synthase can react with monofluoroacetyl-CoA to form a result of fluoroacetate poisoning. Monofluorocitrate is a potent inhibitor of the aconitase reaction. Monofluorocitrate results in a nearly complete block of CAC activity. 23 • Reaction 2: Isomerization of Citrate to Isocitrate via cis-Aconitate Citrate contains 3ry alcoholic group, which is difficult to oxidize. Aconitase generates Isocitrate the 2ry alcoholic compound, which is more readily oxidized. • The reaction involves successive dehydration & hydration, through cis aconitate as a dehydrated intermediate. 24 • Aconitase does not require cofactors, but requires Fe2+ that may be involved in an iron sulfur center, which is an essential in hydration & dehydration activity of aconitase. • Aconitase is highly stereospecific, it operates on that part of citrate derived from oxaloacetate. Therefore; the carbon atoms lost during the first turn of the cycle orginated in oxaloacetate, not acetyl CoA. 25 • Reaction 3: 1st Oxidative Decarboxylation By Isocitrate Dhydrogenase st st • In this step the 1 of 3 NADH & 1 of 2 CO2 are produced by CAC 26 • Isocitrate converted to α-ketogutarate (α-KG) in NAD-dependent oxidative decarboxylation reaction. • ICDH is one of the rate-limiting steps of the CAC cycle. • ICDH required Mn2+ or Mg2+ for Decarboxylation of β-C of Oxalosuccinate. • ICDH is an Isozyme. In mammalian the extramitochondrial form uses NADP+ whereas the intramitochondrial form uses NAD+; however heart mitochondria contain both forms. • ADP is a +ve effectors but ATP & NADH are -ve allosteric effectors. So, at ATP/ADP & NADH/NAD+ ratios, ICDH is inhibited. 27 • Reaction 4: Generation nd of the 2 CO2 by Oxidative Decarboxylation of α- Ketoglutarate (α-Keto- acid) & Formation of Succinyl-CoA: 28 • α-KGDH is multi-enzyme identical to PDH complex, whears α-Keto acid substrate undergoes oxidative decarboxylation, with formation of an acyl-CoA. • They are also similar in their structural features, TPP, lipoic acid, CoASH, FAD & NAD+ participate in the catalytic mechanism. • α-KGDH consists of α-KG dehydrogenase (E1), dihydrolipoy1 trans- succinylase (E2) & dihydrolipoyl dehydrogenase (E3). nd nd • The 2 CO2 & the 2 NADH of the CAC are produced by α-KGDH. • . Unlike PDH, the α-KGDH is not regulated by a protein kinase. • ATP, GTP, NADH & succinyl CoA inhibit α-KGDH. • Ca2+ activate α-KGDH. • Note: the 2 carbon atoms lost as 2 CO2 are not the same as the 2 atoms introduced as acetyl-CoA. 29 • Reaction 5: A Substrate- level Phosphorylation by Succinate Thiokinase (succinyl-CoA synthetase): 30 • Succinly CoA is an energy-rich thiolester similar to acetyl CoA. & its energy is used to drive the formation of an energy-rich phosphate bond GTP at substrate level. GTP drives the synthesis of ATP via nucleoside diphosphokinase: • GTP + ADP →→ GDP + ATP 31 Phase Two: Regeneration of Oxaloacetate • Reaction 6: Oxidation of Succinate to Fumarate by Succinate Dehyrogenase: 32 • FAD is more powerful oxidant than NAD, FAD is used as coenzyme for SDH, because C-C bond is more difficult to oxidize than a C-O bond. • In conjunction with Fe-S center in SDH, it is tightly bound to the mitochondrial inner membrane unlike other CAC enzymes, which are in matrix. This because FADH2, must be reodixidized with the mitochondrial electron transport system, this is to permit the enzyme to act again. • SDH is activated by Succinate. SDH strongly inhibited by Malonate & OAA. There is very close structural
Load more

Recommended publications
  • Arsenite Oxidation by a Hydrogenobaculum Sp. Isolated from Yellowstone National Park by Jessica Donahoe-Christiansen a Thesis Su
    Arsenite oxidation by a Hydrogenobaculum sp. isolated from Yellowstone National Park by Jessica Donahoe-Christiansen A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Land Resources and Environmental Sciences Montana State University © Copyright by Jessica Donahoe-Christiansen (2002) Abstract: A novel Hydrogenobaculum sp. was isolated from an acid-sulfate-chloride geothermal spring in Yellowstone National Park (YNP), WY,USA that had previously been shown to contain microbial populations engaged in arsenite oxidation. Acid-sulfate-chloride thermal springs are a prominent spring type in the Yellowstone geothermal complex and provide unique habitats to study chemolithotrophy where iron, sulfur, arsenic, and perhaps hydrogen gas represent the predominant potential electron donors for generating energy. The organism (designated H55) is an obligate microaerophilic chemolithoautotroph that grows exclusively on hydrogen gas as an electron donor. The optimum temperature and pH for H55 are 55-60°C and 3.0, respectively, and the 16S rDNA sequence of H55 is 98% identical to Hydrogenobaculum acidophilum. Whole cells of H55 displayed Michaelis-Menten type kinetics when oxidizing arsenite, with an estimated Km of 80μM arsenite and a Vmax of 1.47 pM arsenite oxidized / min. (for 1.0 x 10 6 cells per ml). The native habitat of H55 contains large amounts of ferric iron in the stream sediments and high concentrations of aqueous hydrogen sulfide, with concentrations of the latter negatively correlated with arsenite oxidation in the spring. Both chemical species were examined for their contribution to, or influence of, overall (i.e. biotic plus abiotic) stream arsenic redox activity by comparing their effects with arsenite oxidation activities of pure cultures of H55.
    [Show full text]
  • Chemical Name Federal P Code CAS Registry Number Acutely
    Acutely / Extremely Hazardous Waste List Federal P CAS Registry Acutely / Extremely Chemical Name Code Number Hazardous 4,7-Methano-1H-indene, 1,4,5,6,7,8,8-heptachloro-3a,4,7,7a-tetrahydro- P059 76-44-8 Acutely Hazardous 6,9-Methano-2,4,3-benzodioxathiepin, 6,7,8,9,10,10- hexachloro-1,5,5a,6,9,9a-hexahydro-, 3-oxide P050 115-29-7 Acutely Hazardous Methanimidamide, N,N-dimethyl-N'-[2-methyl-4-[[(methylamino)carbonyl]oxy]phenyl]- P197 17702-57-7 Acutely Hazardous 1-(o-Chlorophenyl)thiourea P026 5344-82-1 Acutely Hazardous 1-(o-Chlorophenyl)thiourea 5344-82-1 Extremely Hazardous 1,1,1-Trichloro-2, -bis(p-methoxyphenyl)ethane Extremely Hazardous 1,1a,2,2,3,3a,4,5,5,5a,5b,6-Dodecachlorooctahydro-1,3,4-metheno-1H-cyclobuta (cd) pentalene, Dechlorane Extremely Hazardous 1,1a,3,3a,4,5,5,5a,5b,6-Decachloro--octahydro-1,2,4-metheno-2H-cyclobuta (cd) pentalen-2- one, chlorecone Extremely Hazardous 1,1-Dimethylhydrazine 57-14-7 Extremely Hazardous 1,2,3,4,10,10-Hexachloro-6,7-epoxy-1,4,4,4a,5,6,7,8,8a-octahydro-1,4-endo-endo-5,8- dimethanonaph-thalene Extremely Hazardous 1,2,3-Propanetriol, trinitrate P081 55-63-0 Acutely Hazardous 1,2,3-Propanetriol, trinitrate 55-63-0 Extremely Hazardous 1,2,4,5,6,7,8,8-Octachloro-4,7-methano-3a,4,7,7a-tetra- hydro- indane Extremely Hazardous 1,2-Benzenediol, 4-[1-hydroxy-2-(methylamino)ethyl]- 51-43-4 Extremely Hazardous 1,2-Benzenediol, 4-[1-hydroxy-2-(methylamino)ethyl]-, P042 51-43-4 Acutely Hazardous 1,2-Dibromo-3-chloropropane 96-12-8 Extremely Hazardous 1,2-Propylenimine P067 75-55-8 Acutely Hazardous 1,2-Propylenimine 75-55-8 Extremely Hazardous 1,3,4,5,6,7,8,8-Octachloro-1,3,3a,4,7,7a-hexahydro-4,7-methanoisobenzofuran Extremely Hazardous 1,3-Dithiolane-2-carboxaldehyde, 2,4-dimethyl-, O- [(methylamino)-carbonyl]oxime 26419-73-8 Extremely Hazardous 1,3-Dithiolane-2-carboxaldehyde, 2,4-dimethyl-, O- [(methylamino)-carbonyl]oxime.
    [Show full text]
  • Ketoglutarate Dehydrogenase Complexes of Pseudomonas
    crossmark THE JOURNAL OF BIOLOGICAL CHEMISTRY VOL. 292, NO. 13, pp. 5593–5607, March 31, 2017 © 2017 by The American Society for Biochemistry and Molecular Biology, Inc. Published in the U.S.A. The Pyruvate and ␣-Ketoglutarate Dehydrogenase Complexes of Pseudomonas aeruginosa Catalyze Pyocyanin and Phenazine-1-carboxylic Acid Reduction via the Subunit Dihydrolipoamide Dehydrogenase* Received for publication, December 16, 2016, and in revised form, February 6, 2017 Published, JBC Papers in Press, February 7, 2017, DOI 10.1074/jbc.M116.772848 Nathaniel R. Glasser‡1, Benjamin X. Wang‡2, Julie A. Hoy‡, and Dianne K. Newman‡§3 From the Divisions of ‡Biology and Biological Engineering and §Geology and Planetary Sciences, California Institute of Technology, Pasadena, California 91125 Edited by Joseph Jez Downloaded from Phenazines are a class of redox-active molecules produced by Over a century ago, Pseudomonas aeruginosa was identified diverse bacteria and archaea. Many of the biological functions of as the source of a blue pigment observed in infected wounds (1). phenazines, such as mediating signaling, iron acquisition, and This pigment, a phenazine derivative known as pyocyanin (Fig. http://www.jbc.org/ redox homeostasis, derive from their redox activity. Although 1), was the first natural organic molecule shown to undergo prior studies have focused on extracellular phenazine oxidation one-electron reduction (2–4). This distinctive property by oxygen and iron, here we report a search for reductants and inspired early studies into bacterial respiration. As early as catalysts of intracellular phenazine reduction in Pseudomonas 1931, Friedheim and Michaelis (5, 6) demonstrated that pyocy- aeruginosa. Enzymatic assays in cell-free lysate, together with anin stimulates oxygen consumption and carbon dioxide pro- crude fractionation and chemical inhibition, indicate that duction in both P.
    [Show full text]
  • Enhanced Extraction of Heavy Metals in the Two-Step Process with the Mixed Culture of Lactobacillus Bulgaricus and Streptococcus Thermophilus
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Muroran-IT Academic Resource Archive Enhanced extraction of heavy metals in the two-step process with the mixed culture of Lactobacillus bulgaricus and Streptococcus thermophilus 著者 CHANG Young-Cheol, CHOI DuBok, KIKUCHI Shintaro journal or Bioresource Technology publication title volume 103 number 1 page range 477-480 year 2012-01 URL http://hdl.handle.net/10258/665 doi: info:doi/10.1016/j.biortech.2011.09.059 Enhanced extraction of heavy metals in the two-step process with the mixed culture of Lactobacillus bulgaricus and Streptococcus thermophilus 著者 CHANG Young-Cheol, CHOI DuBok, KIKUCHI Shintaro journal or Bioresource Technology publication title volume 103 number 1 page range 477-480 year 2012-01 URL http://hdl.handle.net/10258/665 doi: info:doi/10.1016/j.biortech.2011.09.059 Enhanced Extraction of Heavy Metals in the Two-Step Process with the Mixed Culture of Lactobacillus bulgaricus and Streptococcus thermophilus Young-Cheol Chang1, DuBok Choi2*, and Shintaro Kikuchi1 1Division of Applied Sciences, College of Environmental Technology, Graduate School of Engineering, Muroran Institute of Technology, 27-1 Mizumoto, Muroran 050-8585, Hokkaido, Japan, 2 Biotechnology Lab, BK Company R&D Center, Gunsan 579-879, and Department of Pharmacy, College of Pharmacy, Chungbuk National University, Cheongju 361-763, Korea. *Corresponding author: DuBok Choi E-mail: [email protected] 1 Abstract For biological extraction of heavy metals from chromated copper arsenate (CCA) treated wood, different bacteria were investigated. The extraction rates of heavy metals using Lactobacillus bulgaricus and Streptococcus thermophilus were highest.
    [Show full text]
  • European Patent Office
    (19) *EP003643305A1* (11) EP 3 643 305 A1 (12) EUROPEAN PATENT APPLICATION (43) Date of publication: (51) Int Cl.: 29.04.2020 Bulletin 2020/18 A61K 31/196 (2006.01) A61K 31/403 (2006.01) A61K 31/405 (2006.01) A61K 31/616 (2006.01) (2006.01) (21) Application number: 18202657.5 A61P 35/00 (22) Date of filing: 25.10.2018 (84) Designated Contracting States: (72) Inventors: AL AT BE BG CH CY CZ DE DK EE ES FI FR GB • LAEMMERMANN, Ingo GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO 1170 Wien (AT) PL PT RO RS SE SI SK SM TR • GRILLARI, Johannes Designated Extension States: 2102 Bisamberg (AT) BA ME • PILS, Vera Designated Validation States: 1160 Wien (AT) KH MA MD TN • GRUBER, Florian 1050 Wien (AT) (71) Applicants: • NARZT, Marie-Sophie • Universität für Bodenkultur Wien 1140 Wien (AT) 1180 Wien (AT) • Medizinische Universität Wien (74) Representative: Loidl, Manuela Bettina et al 1090 Wien (AT) REDL Life Science Patent Attorneys Donau-City-Straße 11 1220 Wien (AT) (54) COMPOSITIONS FOR THE ELIMINATION OF SENESCENT CELLS (57) The invention relates to a composition compris- ing senescent cells. The invention further relates to an ing one or more inhibitors capable of inhibiting at least in vitro method of identifying senescent cells in a subject two of cyclooxygenase-1 (COX-1), cyclooxygenase-2 and to a method of identifying candidate compounds for (COX-2) and lipoxygenase for use in selectively eliminat- the selective elimination of senescent cells. EP 3 643 305 A1 Printed by Jouve, 75001 PARIS (FR) 1 EP 3 643 305 A1 2 Description al.
    [Show full text]
  • Arsenic Transformations
    Structural and mechanistic analysis of the arsenate respiratory reductase provides insight into environmental arsenic transformations Nathaniel R. Glassera, Paul H. Oyalab, Thomas H. Osbornec, Joanne M. Santinic, and Dianne K. Newmana,d,1 aDivision of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125; bDivision of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125; cInstitute of Structural and Molecular Biology, Division of Biosciences, University College London, London WC1E 6BT, United Kingdom; and dDivision of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 Edited by Joan Selverstone Valentine, University of California, Los Angeles, CA, and approved July 13, 2018 (received for review May 9, 2018) Arsenate respiration by bacteria was discovered over two decades A microbe’s capacity for arsenate respiration corresponds ago and is catalyzed by diverse organisms using the well-conserved with the genes encoding the arsenate respiratory reductase (Arr) Arr enzyme complex. Until now, the mechanisms underpinning this complex, present in phylogenetically diverse organisms, includ- metabolism have been relatively opaque. Here, we report the struc- ing Gram-negative and Gram-positive bacteria (13). The ture of an Arr complex (solved by X-ray crystallography to 1.6-Å Arr complex is a member of the DMSO reductase family of resolution), which was enabled by an improved Arr expression molybdoenzymes and comprises two proteins, a large subunit method in the genetically tractable arsenate respirer Shewanella ArrA and a smaller subunit ArrB (13, 14). The ArrA subunit is sp. ANA-3. We also obtained structures bound with the substrate predicted to contain a Mo atom coordinated by a pyranopterin arsenate (1.8 Å), the product arsenite (1.8 Å), and the natural in- guanine dinucleotide cofactor (Mo-bisPGD), as well as a single hibitor phosphate (1.7 Å).
    [Show full text]
  • Metabolic Responses to Arsenite Exposure Regulated Through Histidine Kinases Phor and Aios in Agrobacterium Tumefaciens 5A
    microorganisms Article Metabolic Responses to Arsenite Exposure Regulated through Histidine Kinases PhoR and AioS in Agrobacterium tumefaciens 5A 1, 2, 3 4, Rachel A. Rawle z, Monika Tokmina-Lukaszewska z, Zunji Shi , Yoon-Suk Kang y, Brian P. Tripet 2, Fang Dang 2, Gejiao Wang 3 , Timothy R. McDermott 4, Valerie Copie 2,* and Brian Bothner 2,* 1 Department of Microbiology and Immunology, Montana State University, Bozeman, MT 59717, USA; [email protected] 2 Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717, USA; [email protected] (M.T.-L.); [email protected] (B.P.T.); ff[email protected] (F.D.) 3 State Key Laboratory of Agricultural Microbiology, College of Life Science and Technology, Huazhong Agricultural University, Wuhan 430070, China; [email protected] (Z.S.); [email protected] (G.W.) 4 Department of Land Resources and Environmental Sciences, Montana State University, Bozeman, MT 59717, USA; [email protected] (Y.-S.K.); [email protected] (T.R.M.) * Correspondence: [email protected] (V.C.); [email protected] (B.B.) Current address: Department of Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, y Boston, MA 02215, USA. These authors contributed equally to this work. z Received: 2 July 2020; Accepted: 27 August 2020; Published: 2 September 2020 Abstract: Arsenite (AsIII) oxidation is a microbially-catalyzed transformation that directly impacts arsenic toxicity, bioaccumulation, and bioavailability in environmental systems. The genes for AsIII oxidation (aio) encode a periplasmic AsIII sensor AioX, transmembrane histidine kinase AioS, and cognate regulatory partner AioR, which control expression of the AsIII oxidase AioBA.
    [Show full text]
  • Design and Synthesis of Novel Fluorescence Constructs for The
    DESIGN AND SYNTHESIS OF NOVEL FLUORESCENCE CONSTRUCTS FOR THE DETECTION OF ENVIRONMENTAL ARSENIC by VIVIAN CHIBUZO EZEH (Under the Direction of TODD C. HARROP) ABSTRACT Arsenic compounds are classified as group 1 carcinogens and the maximum contamination level in drinking water is set at 10 ppb by the United States Environmental Protection Agency. Methods currently approved for monitoring environmental arsenic are classified as colorimetric and instrumental methods. However, toxic byproducts (arsine gas and mercury) are formed in colorimetric methods, while instrumental methods require high maintenance costs. Therefore developing a sensitive, safe, and less expensive detection technique for arsenic is needed. One strategy involves the development of new imaging tools using small molecule fluorescent sensors, which will offer a sensitive and inexpensive method of arsenic detection in environmental samples. Emphasis will be on As(III) compounds because they are prevalent in the environment. To accomplish this goal, the coordination chemistry of As(III) was studied to discover new As(III) chemistry/preference for thiols. One finding from this work is the As(III)-promoted redox rearrangement of a benzothiazoline-containing compound to afford a four-coordinate As(III) complex and the benzothiazole analog. The knowledge gained was used to design two fluorescent chemodosimeters for As(III). The first generation sensors, named ArsenoFluors (AFs), were designed to contain a benzothiazoline functional group appended to a coumarin fluorescent reporter and were prepared in high yield by multi-step organic synthesis. The sensors react with As(III) to afford a highly fluorescent coumarin-6 dye (benzothiazole analog), which results in a 20 – 25 fold increase in fluorescence intensity and 0.14 – 0.23 ppb detection limit for As(III) in THF at 298 K.
    [Show full text]
  • Respiratory Arsenate Reductase As a Bidirectional Enzyme
    Biochemical and Biophysical Research Communications 382 (2009) 298–302 Contents lists available at ScienceDirect Biochemical and Biophysical Research Communications journal homepage: www.elsevier.com/locate/ybbrc Respiratory arsenate reductase as a bidirectional enzyme Christine Richey a, Peter Chovanec a,b, Shelley E. Hoeft c, Ronald S. Oremland c, Partha Basu b, John F. Stolz a,* a Department of Biological Sciences, Duquesne University, 600 Forbes Avenue, Pittsburgh, PA 15282, USA b Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, PA 15282, USA c U.S. Geological Survey, 345 Middlefield Rd., MS 480, Menlo Park, CA 94025, USA article info abstract Article history: The haloalkaliphilic bacterium Alkalilimnicola ehrlichii is capable of anaerobic chemolithoautotrophic Received 20 February 2009 growth by coupling the oxidation of arsenite (As(III)) to the reduction of nitrate and carbon dioxide. Anal- Available online 13 March 2009 ysis of its complete genome indicates that it lacks a conventional arsenite oxidase (Aox), but instead pos- sesses two operons that each encode a putative respiratory arsenate reductase (Arr). Here we show that one homolog is expressed under chemolithoautotrophic conditions and exhibits both arsenite oxidase Keywords: and arsenate reductase activity. We also demonstrate that Arr from two arsenate respiring bacteria, Alkal- Arsenite oxidase iphilus oremlandii and Shewanella sp. strain ANA-3, is also biochemically reversible. Thus Arr can function Arsenate reductase as a reductase or oxidase. Its physiological role in a specific organism, however, may depend on the elec- Alkalilimnicola ehrlichii Principle of microscopic reversibility tron potentials of the molybdenum center and [Fe–S] clusters, additional subunits, or constitution of the electron transfer chain.
    [Show full text]
  • Guidance for Assessing Chemical Contaminant Data for Use in Fish Advisories
    United States Office of Water EPA 823-B-00-007 Environmental Protection (4305) November 2000 Agency Guidance for Assessing Chemical Contaminant Data for Use in Fish Advisories Volume 1 Fish Sampling and Analysis Third Edition Guidance for Assessing Chemical Contaminant Data for Use in Fish Advisories Volume 1: Fish Sampling and Analysis Third Edition Office of Science and Technology Office of Water U.S. Environmental Protection Agency Washington, DC United States Environmental Protection Agency (4305) Washington, DC 20460 Official Business Penalty for Private Use $300 Guidance for Assessing Chemical Contamin Volume 1: Fish Sampling and Analysis TABLE OF CONTENTS TABLE OF CONTENTS Section Page Figures ................................................... vii Tables ................................................... ix Acknowledgments .......................................... xii Acronyms ................................................ xiii Executive Summary .......................................ES-1 1 Introduction ........................................... 1-1 1.1 Historical Perspective ............................... 1-1 1.1.1 Establishment of the Fish Contaminant Workgroup . 1-3 1.1.2 Development of a National Fish Advisory Database . 1-3 1.2 Purpose ......................................... 1-10 1.3 Objectives ....................................... 1-13 1.4 Relationship of Manual to Other Guidance Documents ..... 1-15 1.5 Contents of Volume 1 .............................. 1-15 1.6 New Information And Revisions to Volume 1 ............
    [Show full text]
  • Heavier Pnictogens – Treasures for Optical Electronic and Reactivity Tuning Dalton Transactions
    Dalton Volume 48 Number 14 14 April 2019 Pages 4431–4744 Transactions An international journal of inorganic chemistry rsc.li/dalton ISSN 1477-9226 FRONTIER Andreas Orthaber et al. Heavier pnictogens – treasures for optical electronic and reactivity tuning Dalton Transactions View Article Online FRONTIER View Journal | View Issue Heavier pnictogens – treasures for optical electronic and reactivity tuning Cite this: Dalton Trans., 2019, 48, 4460 Joshua P. Green, † Jordann A. L. Wells † and Andreas Orthaber * We highlight recent advances in organopnictogen chemistry contrasting the properties of lighter and heavier pnictogens. Exploring new bonding situations, discovering unprecedented reactivities and produ- cing fascinating opto-electronic materials are some of the most prominent directions of current organo- Received 7th February 2019, pnicogen research. Expanding the chemical toolbox towards the heavier group 15 elements will continue Accepted 19th February 2019 to create new opportunities to tailor molecular properties for small molecule activation/reactivity and DOI: 10.1039/c9dt00574a materials applications alike. This frontier article illustrates the elemental substitution approach in selected rsc.li/dalton literature examples. Creative Commons Attribution 3.0 Unported Licence. Introduction cally realised and fundamental work has continued to fasci- nate researchers around the world. More recently, exciting The discovery of phosphorus by Hennig Brand in 1669 pic- news of arsenic thriving species of bacteria5 have then been tured in the famous painting by Joseph Wright of Derby was disproven to incorporate arsenate.6 On the other hand, newly the beginning of pnictogen (Pn) chemistry (Fig. 1). Discoveries developed synthetic routes have made previously scarce or ffi that followed the incidental P4 preparation included the devel- di cult to handle building blocks readily available, with opment of salvarsan (1), 3-amino-4-hydroxiphenyl arsenic(I), broader applications of these systems now being studied.
    [Show full text]
  • 1,2,3,5,6,8,10,11,16,20,21 Citric Acid Cycle Reactions
    Overview of the citric acid cycle, AKA the krebs cycle AKA tricarboxylic acid AKA TCA cycle Suggested problems from the end of chapter 19: 1,2,3,5,6,8,10,11,16,20,21 Glycogen is broken down into glucose. The reactions of glycolysis result in pyruvate, which is then fed into the citric acid cycle in the form of acetyl CoA. The products of the citric acid cycles are 2 CO2, 3 NADH, 1 FADH2, and 1 ATP or GTP. After pyruvate is generated, it is transported into the mitochondrion, an organelle that contains the citric acid cycle enzymes and the oxidative phosphorylation enzymes. In E. coli, where there are neither mitochondria nor other organelles, these enzymes also seem to be concentrated in certain regions in the cell. Citric acid cycle reactions Overall, there are 8 reactions that result in oxidation of the metabolic fuel. This results in reduction of NAD+ and FAD. NADH and FADH2 will transfer their electrons to oxygen during oxidative phosphorylation. •In 1936 Carl Martius and Franz Knoop showed that citrate can be formed non-enzymaticly from Oxaloacetate and pyruvate. •In 1937 Hans Krebs used this information for biochemical experiments that resulted in his suggestion that citrate is processed in an ongoing circle, into which pyruvate is “fed.” •In 1951 it was shown that it was acetyl Coenzyme-A that condenses with oxaloacetate to form citrate. 1 The pre-citric acid reaction- pyruvate dehydrogenase Pyruvate dehydrogenase is a multi-subunit complex, containing three enzymes that associate non-covalently and catalyze 5 reaction. The enzymes are: (E1) pyruvate dehydrogenase (E2) dihydrolipoyl transacetylase (E3) dihydrolipoyl dehydrogenase What are the advantages for arranging enzymes in complexes? E.
    [Show full text]