Biochemistry Metabolism

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Biochemistry Metabolism 07.11.2017 – 27.11.2017 Nucleotide Metabolism Gerhild van Echten-Deckert Tel. 73 2703 E-mail: [email protected] www.limes-institut-bonn.de NADPH-dependent reduction of ribonucleotides to deoxyribonucleotides Nelson, Cox: Lehninger Biochemistry Ribonucleotide reductase: the key to the DNA-world Nelson, Cox: Lehninger Biochemistry Catalytic mechanism of ribonucleotide reductase + Nelson, Cox: Lehninger Biochemistry Complex regulation of ribonucleotide reductase by (d)NTPs Nelson, Cox: Lehninger Biochemistry Biosynthesis of thymidylate (dTMP) via dUTP Nelson, Cox: Lehninger Biochemistry Thymidylate synthase catalyses conversion of dUMP to dTMP CH2 H Löffler & Petrides, Biochemie und Pathobiochemie Anticancer Drug Targets Antibiotic Berg, Tymoczko, Stryer: Biochemistry Catabolism of purine nucleotides (dAdenosine) Physiological importance of uric acid! Immune deficiency: Adenosine-deaminase (ADA) defect! Voet, Voet: Biochemistry Uric Acid: The Oxidant-Anitoxidant Paradox Early 1980s hypothesis: Silencing of the uricase gene with an increased blood level of uric acid provided an evolutionary advantage. In vitro experiments: uric acid is a powerful scavenger of singlet oxygen, peroxyl radicals and hydroxyl radicals. Thus it protects as a major antioxidant of plasma from ox. damage thus increasing life span and decreasing the risk for cancer. Epidemiologic studies beginning of 21st century: Cardiovascular disease, hypertension, metabolic syndrome are strongly associated with high blood levels of uric acid and in many cases predict development of hypertension, visceral obesity, insulin resistance, diabetes typeII, kidney disease, cardiovascular events. Nucleosides, Nucleotides, Nucleic Acids (2008) 27:608-19 Allopurinol, an inhibitor of xanthine oxidase prevents crystalline deposits of uric acid (gout) = Alloxanthine: Sticks in the active site of XO => suicide inhibitor Nelson, Cox: Lehninger Biochemistry Catabolism of pyrimidine nucleotides Voet, Voet: Biochemistry De novo and salvage pathways for nucleotide synthesis Spina bifida (folate deficiency) Lesch-Nyhan syndrome: hereditary disease (HGPRT-deficiency) Lodish et al. Molecular Biology of the Cell The purine nucleotide cycle: anaplerotic function in skeletal muscle Pathology: Myoadenylatedeaminase Net: Asp + GTP + H O Fumarate + GDP + P 2 i Voet, Voet: Biochemistry.

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Nucleotide Degradation
Nucleotide Degradation Nucleotide Degradation The Digestion Pathway • Ingestion of food always includes nucleic acids. • As you know from BI 421, the low pH of the stomach does not affect the polymer. • In the duodenum, zymogens are converted to nucleases and the nucleotides are converted to nucleosides by non-specific phosphatases or nucleotidases. nucleases • Only the non-ionic nucleosides are taken & phospho- diesterases up in the villi of the small intestine. Duodenum Non-specific phosphatases • In the cell, the first step is the release of nucleosides) the ribose sugar, most effectively done by a non-specific nucleoside phosphorylase to give ribose 1-phosphate (Rib1P) and the free bases. • Most ingested nucleic acids are degraded to Rib1P, purines, and pyrimidines. 1 Nucleotide Degradation: Overview Fate of Nucleic Acids: Once broken down to the nitrogenous bases they are either: Nucleotides 1. Salvaged for recycling into new nucleic acids (most cells; from internal, Pi not ingested, nucleic Nucleosides acids). Purine Nucleoside Pi aD-Rib 1-P (or Rib) 2. Oxidized (primarily in the Phosphorylase & intestine and liver) by first aD-dRib 1-P (or dRib) converting to nucleosides, Bases then to –Uric Acid (purines) –Acetyl-CoA & Purine & Pyrimidine Oxidation succinyl-CoA Salvage Pathway (pyrimidines) The Salvage Pathways are in competition with the de novo biosynthetic pathways, and are both ANABOLISM Nucleotide Degradation Catabolism of Purines Nucleotides: Nucleosides: Bases: 1. Dephosphorylation (via 5’-nucleotidase) 2. Deamination and hydrolysis of ribose lead to production of xanthine. 3. Hypoxanthine and xanthine are then oxidized into uric acid by xanthine oxidase. Spiders and other arachnids lack xanthine oxidase.
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35 Disorders of Purine and Pyrimidine Metabolism
35 Disorders of Purine and Pyrimidine Metabolism Georges van den Berghe, M.- Françoise Vincent, Sandrine Marie 35.1 Inborn Errors of Purine Metabolism – 435 35.1.1 Phosphoribosyl Pyrophosphate Synthetase Superactivity – 435 35.1.2 Adenylosuccinase Deficiency – 436 35.1.3 AICA-Ribosiduria – 437 35.1.4 Muscle AMP Deaminase Deficiency – 437 35.1.5 Adenosine Deaminase Deficiency – 438 35.1.6 Adenosine Deaminase Superactivity – 439 35.1.7 Purine Nucleoside Phosphorylase Deficiency – 440 35.1.8 Xanthine Oxidase Deficiency – 440 35.1.9 Hypoxanthine-Guanine Phosphoribosyltransferase Deficiency – 441 35.1.10 Adenine Phosphoribosyltransferase Deficiency – 442 35.1.11 Deoxyguanosine Kinase Deficiency – 442 35.2 Inborn Errors of Pyrimidine Metabolism – 445 35.2.1 UMP Synthase Deficiency (Hereditary Orotic Aciduria) – 445 35.2.2 Dihydropyrimidine Dehydrogenase Deficiency – 445 35.2.3 Dihydropyrimidinase Deficiency – 446 35.2.4 Ureidopropionase Deficiency – 446 35.2.5 Pyrimidine 5’-Nucleotidase Deficiency – 446 35.2.6 Cytosolic 5’-Nucleotidase Superactivity – 447 35.2.7 Thymidine Phosphorylase Deficiency – 447 35.2.8 Thymidine Kinase Deficiency – 447 References – 447 434 Chapter 35 · Disorders of Purine and Pyrimidine Metabolism Purine Metabolism Purine nucleotides are essential cellular constituents 4 The catabolic pathway starts from GMP, IMP and which intervene in energy transfer, metabolic regula- AMP, and produces uric acid, a poorly soluble tion, and synthesis of DNA and RNA. Purine metabo- compound, which tends to crystallize once its lism can be divided into three pathways: plasma concentration surpasses 6.5–7 mg/dl (0.38– 4 The biosynthetic pathway, often termed de novo, 0.47 mmol/l). starts with the formation of phosphoribosyl pyro- 4 The salvage pathway utilizes the purine bases, gua- phosphate (PRPP) and leads to the synthesis of nine, hypoxanthine and adenine, which are pro- inosine monophosphate (IMP).
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The Regulation of Carbamoyl Phosphate Synthetase-Aspartate Transcarbamoylase-Dihydroorotase (Cad) by Phosphorylation and Protein-Protein Interactions
THE REGULATION OF CARBAMOYL PHOSPHATE SYNTHETASE-ASPARTATE TRANSCARBAMOYLASE-DIHYDROOROTASE (CAD) BY PHOSPHORYLATION AND PROTEIN-PROTEIN INTERACTIONS Eric M. Wauson A dissertation submitted to the faculty of the University of North Carolina at Chapel Hill in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Pharmacology. Chapel Hill 2007 Approved by: Lee M. Graves, Ph.D. T. Kendall Harden, Ph.D. Gary L. Johnson, Ph.D. Aziz Sancar M.D., Ph.D. Beverly S. Mitchell, M.D. 2007 Eric M. Wauson ALL RIGHTS RESERVED ii ABSTRACT Eric M. Wauson: The Regulation of Carbamoyl Phosphate Synthetase-Aspartate Transcarbamoylase-Dihydroorotase (CAD) by Phosphorylation and Protein-Protein Interactions (Under the direction of Lee M. Graves, Ph.D.) Pyrimidines have many important roles in cellular physiology, as they are used in the formation of DNA, RNA, phospholipids, and pyrimidine sugars. The first rate- limiting step in the de novo pyrimidine synthesis pathway is catalyzed by the carbamoyl phosphate synthetase II (CPSase II) part of the multienzymatic complex Carbamoyl phosphate synthetase, Aspartate transcarbamoylase, Dihydroorotase (CAD). CAD gene induction is highly correlated to cell proliferation. Additionally, CAD is allosterically inhibited or activated by uridine triphosphate (UTP) or phosphoribosyl pyrophosphate (PRPP), respectively. The phosphorylation of CAD by PKA and ERK has been reported to modulate the response of CAD to allosteric modulators. While there has been much speculation on the identity of CAD phosphorylation sites, no definitive identification of in vivo CAD phosphorylation sites has been performed. Therefore, we sought to determine the specific CAD residues phosphorylated by ERK and PKA in intact cells.
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Xanthine Oxidase Assay (XO) Cat
Xanthine Oxidase Assay (XO) Cat. No. 8458 100 Tests in 96-well plate Introduction Xanthine Oxidase (XO) located predominantly in the liver and intestine in mammalian tissues and catalyzes the hydroxylation of hypoxanthine to xanthine and then to uric acid and hydrogen peroxide. XO activity is normally very low in blood and liver injury can result in the release of XO into blood. XO activity or expression can be up-regulated in gout and cardiovascular disease. This colorimetric assay is based on XO-catalyzed oxidation of xanthine, in which the formed hydrogen peroxide is catalyzed by peroxidase and reacts with 4-aminoantipyrine to form the product dye. The color intensity of the reaction product at 550nm is directly proportional to XO activity in the sample. Kit Components Cat. No. # of vials Reagent Quantity Storage 8458a 1 Assay buffer 10 mL 4°C 8458b 1 Xanthine Oxidase standard 0.2 mL -20°C 8458c 1 Xanthine 2.0 mL -20°C 8458d 1 Substrate mix 1.6 mL -20°C 8458e 1 Enzyme mix 0.1 mL -20°C Product Use The Xanthine Oxidase Assay kit measures the xanthine oxidase level of different types of samples, such as serum, plasma, tissues. This product is for research purposes only and not for use in animals, humans, or diagnostic procedures. Quality Control Serially diluted xanthine oxidase solutions with concentrations ranging from 7.81 to 125 mU/mL are measured with the ScienCell™ Xanthine Oxidase Assay kit. The increase in OD550nm is monitored as a function of time (Figure 1) and the resulting standard curve of ∆OD550nm/min vs xanthine oxidase activity are plotted (Figure 2).
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Difluorodeoxyguanosine in Chinese Hamster Ovary Cells'
[CANCER RESEARCH55, 1517-1524, April 1, 19951 Cytotoxicity, Metabolism, and Mechanisms of Action of 2',2'- Difluorodeoxyguanosine in Chinese Hamster Ovary Cells' Varsha Gandhi,2 Shin Mineishi, Peng Huang, Amy J. Chapman, Yandan Yang, Feng Chen, Biffie Nowak, Shern Chubb, Larry W. Hertel, and William Plunkett Department of Clinical Investigation, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030 (V. G., S. M., P. H.. A. J. C.. Y. 1'., F. C., B. N., S. C., w. p.]. andLillyResearchLaboratories,Indianapolis,indiana46285(L W.H.) ABSTRACT treatment of hematological malignancies (4â€”6).Arabinosyladenine, although not successful in cancer therapy, has proven antiviral activity The emerging clinical success of gemcItabine (2',2'-difluorodeoxycytl dine) Stimulated interest in the synthesis and evaluation of purine conge (7). The importance of the 2'-pentose moiety for the design of chemo ners. The cytotoxicity, metabolism, and mechanisms of action of the lead therapeutic agents and the fact that fluorine has a van der Waals radius candidate, 2',2'-difluorodeoxyguanoslne (dFdGuo), were StUdied In ChI nese hamster ovary cells Unlike the natural nucleoside deoxyguanosine similar to that of hydrogen led to the synthesis and evaluation of (dGuo), dFdGuo was not a substrate for purine nucleoside phosphorylase 2'-fluorinated analogues. 2'-Deoxy-2'-fluorocytidine and 2'-deoxy Wild-type Chinese hamster ovary cells and a mutant line deficient in 2'-fluoroguanosine possess inhibitory activities against several deoxycytidine (dCyd) kinase were similarly affected by dFdGuo (50% lymphoid cell lines and influenza viruses, respectively (8, 9). Inter inhibitory concentration, 7.5 and 6.5 pM, respectively), suggesting that estingly, substitution of the 2'-hydrogen of dCyd3 with a fluorine unlike gemcitabine, dCyd kinase was not responsible for activation of atom in the arabinose configuration produced 10-fold greater cyto dFdGuo This was further confirmed by separation of nucleoside kinases toxicity than when placed in the ribose position (10).
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DHFR Inhibitors: Reading the Past for Discovering Novel Anticancer Agents
molecules Review DHFR Inhibitors: Reading the Past for Discovering Novel Anticancer Agents Maria Valeria Raimondi 1,*,† , Ornella Randazzo 1,†, Mery La Franca 1 , Giampaolo Barone 1 , Elisa Vignoni 2, Daniela Rossi 2 and Simona Collina 2,* 1 Department of Biological, Chemical and Pharmaceutical Sciences and Technologies (STEBICEF), University of Palermo, via Archirafi 32, 90123 Palermo, Italy; [email protected] (O.R.); [email protected] (M.L.F.); [email protected] (G.B.) 2 Drug Sciences Department, Medicinal Chemistry and Pharmaceutical Technology Section, University of Pavia, via Taramelli 12, 27100 Pavia, Italy; [email protected] (E.V.); [email protected] (D.R.) * Correspondence: [email protected] (M.V.R.); [email protected] (S.C.); Tel.: +390-912-389-1915 (M.V.R.); +390-382-987-379 (S.C.) † These Authors contributed equally to this work. Academic Editors: Simona Collina and Mariarosaria Miloso Received: 25 February 2019; Accepted: 20 March 2019; Published: 22 March 2019 Abstract: Dihydrofolate reductase inhibitors are an important class of drugs, as evidenced by their use as antibacterial, antimalarial, antifungal, and anticancer agents. Progress in understanding the biochemical basis of mechanisms responsible for enzyme selectivity and antiproliferative effects has renewed the interest in antifolates for cancer chemotherapy and prompted the medicinal chemistry community to develop novel and selective human DHFR inhibitors, thus leading to a new generation of DHFR inhibitors. This work summarizes the mechanism of action, chemical, and anticancer profile of the DHFR inhibitors discovered in the last six years. New strategies in DHFR drug discovery are also provided, in order to thoroughly delineate the current landscape for medicinal chemists interested in furthering this study in the anticancer field.
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Xanthine Oxidoreductase in Cancer
Cancer Medicine Open Access REVIEW Xanthine oxidoreductase in cancer: more than a differentiation marker Maria Giulia Battelli, Letizia Polito, Massimo Bortolotti & Andrea Bolognesi Department of Experimental, Diagnostic and Specialty Medicine – DIMES, Alma Mater Studiorum – University of Bologna, General Pathology Unit, Via S. Giacomo 14, 40126 Bologna, Italy Keywords Abstract Differentiation, oncogenesis, reactive oxygen and nitrogen species, uric acid, xanthine Human xanthine oxidoreductase (XOR) catalyzes the last two steps of purine oxidoreductase catabolism and is present in two interconvertible forms, which may utilize O2 or NAD+ as electron acceptors. In addition to uric acid, XOR products may Correspondence comprise reactive oxygen and nitrogen species that have many biologic effects, Letizia Polito, Department of Experimental, including inflammation, endothelial dysfunction, and cytotoxicity, as well as Diagnostic and Specialty Medicine – DIMES, mutagenesis and induction of proliferation. XOR is strictly modulated at the Alma Mater Studiorum – University of Bologna, General Pathology Unit, Via S. transcriptional and post-translational levels, and its expression and activity are Giacomo 14, 40126 Bologna, Italy. highly variable in cancer. Xanthine oxidoreductase (XOR) expression has been Tel: +39 051 2094700; Fax: +39 051 2094746; negatively associated with a high malignity grade and a worse prognosis in E-mail: [email protected] neoplasms of the breast, liver, gastrointestinal tract, and kidney, which normally express a high level of XOR protein. However, the level of XOR expression Funding Information may be associated with a worse outcome in cancer of low XOR-expressing cells, This work was supported by the Pallotti in relation to the inflammatory response elicited through the tissue damage Legacies for Cancer Research.
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1611 REGULATION of PYRIMIDINE METABOLISM in PLANTS Chris
[Frontiers in Bioscience 9, 1611-1625, May 1, 2004] REGULATION OF PYRIMIDINE METABOLISM IN PLANTS 1, 2 1, 3 1, 4 1, 5 1, 6 1, 7 Chris Kafer , Lan Zhou , Djoko Santoso , Adel Guirgis , Brock Weers , Sanggyu Park and Robert Thornburg 1 1 Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa 50011, 2 BASF Plant Science LLC, 2901 South Loop Drive, Ste 3800, Ames, Iowa 50014, 3 Lan Zhou, Pioneer Hi-Bred International, Inc. 7300 NW 62nd Avenue, PO Box 1004, Johnston, Iowa 50131-1004, 4 Indonesian Biotechnology Research Institute for Estate Crops, Jl, Taman Kencana No 1, Bogor 16151 Indonesia, 5 Institute of Genetic Engineering and Biotechnology, Menofiya University, PO Box 79/22857, Sadat City, Egypt, 6 Department of Biochemistry, University of Iowa, 4/511 Bowen Science Building, Iowa City, Iowa 52242-1109, 7 Division of Life and Environment, College of Natural Resources, Daegu University, Gyongsan City, Gyongbuk, Korea 712-714 TABLE OF CONTENTS 1. Abstract 2. Introduction 3. Pyrimidine metabolic pathways 3.1. De novo pyrimidine biosynthesis 3.1.1. CPSase 3.1.2. ATCase 3.1.3. DHOase 3.1.4. DHODH 3.1.5. UMPS 3.1.6. Intracellular Organization of the de novo Pathway 3.2. Pyrimidine Salvage and Recycling 3.2.1. Cytosine deaminase 3.2.2. Cytidine deaminase 3.2.3. UPRTase 3.3. Pyrimidine Modification 3.3.1. UMP/CMP kinase 3.3.2. NDP kinase 3.3.3. CTP synthase, NDP reductase, dUTPase 3.3.4. Thymidylate synthase/Dihydrofolate reductase 3.4. Pyrimidine Catabolism 4. Regulation of pyrimidine metabolism 4.1.
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TITLE Adenylate Kinase 2 Deficiency Causes NAD+ Depletion and Impaired Purine Metabolism During Myelopoiesis
bioRxiv preprint doi: https://doi.org/10.1101/2021.07.05.450633; this version posted July 6, 2021. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC-ND 4.0 International license. TITLE Adenylate Kinase 2 deficiency causes NAD+ depletion and impaired purine metabolism during myelopoiesis AUTHORS Wenqing Wang1, Andew DeVilbiss2, Martin Arreola1, Thomas Mathews2, Misty Martin-Sandoval2, Zhiyu Zhao2, Avni Awani1, Daniel Dever1, Waleed Al-Herz3, Luigi Noratangelo4, Matthew H. Porteus1, Sean J. Morrison2, Katja G. Weinacht1, * 1. Department of Pediatrics, Stanford University School of Medicine, Stanford, California 94305 USA 2. Children’s Research Institute, University of Texas Southwestern Medical Center, Dallas, Texas 75390 USA 3. Department of Pediatrics, Faculty of Medicine, Kuwait University, Safat, 13110 Kuwait 4. Laboratory of Clinical Immunology and Microbiology, National Institute of Health, BETHESDA MD 20814 USA * Corresponding author ABSTRACT Reticular Dysgenesis is a particularly grave from of severe combined immunodeficiency (SCID) that presents with severe congenital neutropenia and a maturation arrest of most cells of the lymphoid lineage. The disease is caused by biallelic loss of function mutations in the mitochondrial enzyme Adenylate Kinase 2 (AK2). AK2 mediates the phosphorylation of adenosine monophosphate (AMP) to adenosine diphosphate (ADP) as substrate for adenosine triphosphate (ATP) synthesis in the mitochondria. Accordingly, it has long been hypothesized that a decline in OXPHOS metabolism is the driver of the disease. The mechanistic basis for Reticular Dysgenesis, however, remained incompletely understood, largely due to lack of appropriate model systems to phenocopy the human disease.
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Monitoring the Redox Status in Multiple Sclerosis
Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 31 July 2020 doi:10.20944/preprints202007.0737.v1 Review Monitoring the Redox Status in Multiple Sclerosis Masaru Tanaka 1,2 and László Vécsei 1,2,* 1 MTA-SZTE, Neuroscience Research Group, Semmelweis u. 6, Szeged, H-6725 Hungary; [email protected] 2 Department of Neurology, Interdisciplinary Excellence Centre, Faculty of Medicine, University of Szeged, Semmelweis u. 6, H-6725 Szeged, Hungary * Correspondence: [email protected]; Tel.: +36-62-545-351 Received: date; Accepted: date; Published: date Abstract: Worldwide, over 2.2 million people are suffered from multiple sclerosis (MS), a multifactorial demyelinating disease of the central nervous system, characterized by multifocal inflammatory or demyelinating attacks associated with neuroinflammation and neurodegeneration. The blood, cerebrospinal fluid, and postmortem brain samples of MS patients evidenced the presence of reduction-oxidation (redox) homeostasis disturbance such as the alternations of oxidative and antioxidative enzyme activities and the presence of degradation products. This review article discussed the components of redox homeostasis including reactive chemical species, oxidative enzymes, antioxidative enzymes, and degradation products. The reactive chemical species covered frequently discussed reactive oxygen/nitrogen species, rarely featured reactive chemicals such as sulfur, carbonyls, halogens, selenium, and nucleophilic species that potentially act as reductive as well as pro-oxidative stressors. The antioxidative enzyme systems covered the nuclear factor erythroid-2-related factor 2 (NRF2)-Kelch-like ECH-associated protein 1 (KEAP1) signaling pathway, a possible biomarker sensitive to the initial phase of oxidative stress. Altered components of the redox homeostasis in MS were discussed, some of which turned to be MS subtype- or treatment-specific and thus potentially become diagnostic, prognostic, predictive, and/or therapeutic biomarkers.
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NADPH Homeostasis in Cancer: Functions, Mechanisms and Therapeutic Implications
Signal Transduction and Targeted Therapy www.nature.com/sigtrans REVIEW ARTICLE OPEN NADPH homeostasis in cancer: functions, mechanisms and therapeutic implications Huai-Qiang Ju 1,2, Jin-Fei Lin1, Tian Tian1, Dan Xie 1 and Rui-Hua Xu 1,2 Nicotinamide adenine dinucleotide phosphate (NADPH) is an essential electron donor in all organisms, and provides the reducing power for anabolic reactions and redox balance. NADPH homeostasis is regulated by varied signaling pathways and several metabolic enzymes that undergo adaptive alteration in cancer cells. The metabolic reprogramming of NADPH renders cancer cells both highly dependent on this metabolic network for antioxidant capacity and more susceptible to oxidative stress. Modulating the unique NADPH homeostasis of cancer cells might be an effective strategy to eliminate these cells. In this review, we summarize the current existing literatures on NADPH homeostasis, including its biological functions, regulatory mechanisms and the corresponding therapeutic interventions in human cancers, providing insights into therapeutic implications of targeting NADPH metabolism and the associated mechanism for cancer therapy. Signal Transduction and Targeted Therapy (2020) 5:231; https://doi.org/10.1038/s41392-020-00326-0 1234567890();,: BACKGROUND for biosynthetic reactions to sustain their rapid growth.5,11 This In cancer cells, the appropriate levels of intracellular reactive realization has prompted molecular studies of NADPH metabolism oxygen species (ROS) are essential for signal transduction and and its exploitation for the development of anticancer agents. cellular processes.1,2 However, the overproduction of ROS can Recent advances have revealed that therapeutic modulation induce cytotoxicity and lead to DNA damage and cell apoptosis.3 based on NADPH metabolism has been widely viewed as a novel To prevent excessive oxidative stress and maintain favorable and effective anticancer strategy.
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Nucleotide Metabolism II
Nucleotide Metabolism II • Biosynthesis of deoxynucleotides • Salvage Pathway • Catabolism: Purines • Catabolism: Pyrimidines • Feedback inhibition in purine nucleotide biosynthesis CPS II • Cytosolic CPS II uses glutamine as the nitrogen donor to carbamoyl phosphate Regulation of pyrimidine synthesis •CPSII is allosterically regulated: PRPP and IMP are activators Several pyrimidines are inhibitors • Aspartate transcarbamoylase (ATCase) Important regulatory point in prokaryotes Catalyzes the first committed pathway step Allosteric regulators: CTP (-), CTP + UTP (-), ATP (+) • Regulation of pyrimidine nucleotide synthesis in E. coli Biosynthesis of deoxynucleotides • Uses diphosphates (ribo) • Ribonucleotide reducatase • 2 sub-units • R1- reduces, active and two allosteric sites (activity and specificity site) • R2- tyrosine radical carries electrons • removes 2' OH to H Ribonucleotide reductase reaction • removes 2' OH to H • Thioredoxin and NADPH used to regenerate sulfhydryl groups Thymidylate synthesis • UDP ------> dUMP • dUMP --------> dTMP • required THF • methylates uracil Regulation THF • Mammals cannot conjugate rings or synthesize PABA. • So must get in diet. • Sulfonamides effective in bacteria due to competitive inhibition of the incorporation of PABA Cancer Drugs • fluorouracil-- suicide inhibitor of Thy synthase • aminopterin • Methotrexate -- inhibits DHF reductase Salvage of Purines and Pyrimidines • During cellular metabolism or digestion, nucleic acids are degraded to heterocyclic bases • These bases can be salvaged
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