DOCSLIB.ORG

Glycogen Metabolism CH2OH CH2OH Glycogen H O H H O H H H OH H OH H 1 O OH O H OH H OH

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Glycogen Metabolism CH2OH CH2OH Glycogen H O H H O H H H OH H OH H 1 O OH O H OH H OH Glycogen Metabolism CH2OH CH2OH glycogen H O H H O H H H OH H OH H 1 O OH O H OH H OH CH2OH CH2OH 6CH2 CH2OH CH2OH H O H H O H H 5 O H H O H H O H H H H H H 1 4 OH H OH H 4 OH H OH H OH H O O O O OH OH 3 2 H OH H OH H OH H OH H OH Glycogen is a polymer of glucose residues linked by a(14) glycosidic bonds, mainly a(16) glycosidic bonds, at branch points. Glycogen chains & branches are longer than shown. Glucose is stored as glycogen predominantly in liver and muscle cells. Glycogen Glucose Hexokinase or Glucokinase Glucose-6-Pase Glucose-1-P Glucose-6-P Glucose + Pi Glycolysis Pathway Pyruvate Glucose metabolism in liver. Glucose-6-phosphate may enter Glycolysis or (mainly in liver) be dephosphorylated for release to the blood. Glycogenesis Definition: synthesis of glycogen from glucose. Site: cytosol of liver & muscles. Steps: O CH2OH HN H O H Glycogen H O N O O synthesis OH H OH O P O P O CH 2 O H OH O O H H H H UDP-glucose OH OH Uridine diphosphate glucose (UDP-glucose) is the immediate precursor for glycogen synthesis. As glucose residues are added to glycogen, UDP-glucose is the substrate and UDP is released as a reaction product. UDP-Glucose Pyrophosphorylase O CH2OH HN H O H H O N OH H O O O O OH O P O + O P O P O P O CH2 O H OH O O O O H H glucose-1-phosphate H H UTP OH OH PPi O CH2OH HN H O H H O N OH H O O OH O P O P O CH 2 O H OH O O H H H H UDP-glucose OH OH Glycogen Synthase catalyzes transfer of the glucose moiety of UDP-glucose to the hydroxyl at C4 of the terminal residue of a glycogen chain to form an a(1 4) glycosidic linkage: glycogen(n residues) + UDP-glucose glycogen(n +1 residues) + UDP Glycogen Synthase then catalyzes elongation of glycogen chains A branching enzyme transfers a segment from the end of a glycogen chain to the C6 hydroxyl of a glucose residue of glycogen to yield a branch with an a(16) linkage. Regulation of glycogenesis Glycogen Synthase is allosterically activated by glucose-6-P (opposite of effect on Phosphorylase). Thus Glycogen Synthase is active when high blood glucose leads to elevated intracellular glucose-6-P. It is useful to a cell to store glucose as glycogen when the input to Glycolysis (glucose-6-P), and the main product of Glycolysis (ATP), are adequate. Glycogenolysis Definition: breakdown of glycogen to glucose in liver or G6P in muscles ( due to absence of G6 phosphatase in muscles). Importance: In muscles: source of energy during exercise. In liver: source of blood glucose during 18 hours starvation. Steps: Glycogen catabolism Glycogen Phosphorylase catalyzes phosphorolytic cleavage of the a(14) glycosidic linkages of glycogen, releasing glucose-1-phosphate as reaction product. Debranching enzyme has 2 independent active sites, consisting of residues in different segments of a single polypeptide chain: The transferase of the debranching enzyme transfers 3 glucose residues from a 4-residue limit branch to the end of another branch, diminishing the limit branch to a single glucose residue. The a(16) glucosidase moiety of the debranching enzyme then catalyzes hydrolysis of the a(16) linkage, yielding free glucose. This is a minor fraction of glucose released from glycogen. The major product of glycogen breakdown is glucose-1-phosphate, from Phosphorylase activity. Regulation of glycogenolysis Glycogen Phosphorylase in muscle is subject to allosteric regulation by AMP, ATP, and glucose-6-phosphate. AMP (present significantly when ATP is depleted) activates Phosphorylase ATP & glucose-6-phosphate inhibit Phosphorylase Thus glycogen breakdown is inhibited when ATP and glucose-6- phosphate are plentiful. SUMMARY The Metabolism of Glycogen in Animals 1. Glycogen is stored in muscle and liver as large particles. Contained within the particles are the enzymes that metabolize glycogen, as well as regulatory enzymes. 2. Glycogen phosphorylase catalyzes phosphorolytic cleavage at the nonreducing ends of glycogen chains, producing glucose 1-phosphate. The debranching enzyme transfers branches onto main chains and releases the residue at the (a1→6) branch as free glucose. SUMMARY The Metabolism of Glycogen in Animals (cont.) 3. Phosphoglucomutase interconverts glucose 1- phosphate and glucose 6-phosphate. Glucose 6- phosphate can enter glycolysis or, in liver, can be converted to free glucose by glucose 6- phosphatase in the endoplasmic reticulum, then released to replenish blood glucose. SUMMARY The Metabolism of Glycogen in Animals (cont.) 4. The sugar nucleotide UDP-glucose donates glucose residues to the nonreducing end of glycogen in the reaction catalyzed by glycogen synthase. A separate branching enzyme produces the a(1→6) linkages at branch points. SUMMARY The Metabolism of Glycogen in Animals (cont.) 5. New glycogen particles begin with the autocatalytic formation of a glycosidic bond between the glucose of UDP-glucose and a Tyr residue in the protein glycogenin, followed by addition of several glucose residues to form a primer that can be acted upon by glycogen synthase. .
Load more

Recommended publications
  • Carbohydrates: Structure and Function
    CARBOHYDRATES: STRUCTURE AND FUNCTION Color index: . Very important . Extra Information. “ STOP SAYING I WISH, START SAYING I WILL” 435 Biochemistry Team *هذا العمل ﻻ يغني عن المصدر المذاكرة الرئيسي • The structure of carbohydrates of physiological significance. • The main role of carbohydrates in providing and storing of energy. • The structure and function of glycosaminoglycans. OBJECTIVES: 435 Biochemistry Team extra information that might help you 1-synovial fluid: - It is a viscous, non-Newtonian fluid found in the cavities of synovial joints. - the principal role of synovial fluid is to reduce friction between the articular cartilage of synovial joints during movement O 2- aldehyde = terminal carbonyl group (RCHO) R H 3- ketone = carbonyl group within (inside) the compound (RCOR’) 435 Biochemistry Team the most abundant organic molecules in nature (CH2O)n Carbohydrates Formula *hydrate of carbon* Function 1-provides important part of energy Diseases caused by disorders of in diet . 2-Acts as the storage form of energy carbohydrate metabolism in the body 3-structural component of cell membrane. 1-Diabetesmellitus. 2-Galactosemia. 3-Glycogen storage disease. 4-Lactoseintolerance. 435 Biochemistry Team Classification of carbohydrates monosaccharides disaccharides oligosaccharides polysaccharides simple sugar Two monosaccharides 3-10 sugar units units more than 10 sugar units Joining of 2 monosaccharides No. of carbon atoms Type of carbonyl by O-glycosidic bond: they contain group they contain - Maltose (α-1, 4)= glucose + glucose -Sucrose (α-1,2)= glucose + fructose - Lactose (β-1,4)= glucose+ galactose Homopolysaccharides Heteropolysaccharides Ketone or aldehyde Homo= same type of sugars Hetero= different types Ketose aldose of sugars branched unBranched -Example: - Contains: - Contains: Examples: aldehyde group glycosaminoglycans ketone group.
    [Show full text]
  • Carbohydrates Adapted from Pellar
    Carbohydrates Adapted from Pellar OBJECTIVE: To learn about carbohydrates and their reactivities BACKGROUND: Carbohydrates are a major food source, with most dietary guidelines recommending that 45-65% of daily calories come from carbohydrates. Rice, potatoes, bread, pasta and candy are all high in carbohydrates, specifically starches and sugars. These compounds are just a few examples of carbohydrates. Other carbohydrates include fibers such as cellulose and pectins. In addition to serving as the primary source of energy for the body, sugars play a number of other key roles in biological processes, such as forming part of the backbone of DNA structure, affecting cell-to-cell communication, nerve and brain cell function, and some disease pathways. Carbohydrates are defined as polyhydroxy aldehydes or polyhydroxy ketones, or compounds that break down into these substances. They can be categorized according to the number of carbons in the structure and whether a ketone or an aldehyde group is present. Glucose, for example, is an aldohexose because it contains six carbons and an aldehyde functional group. Similarly, fructose would be classified as a ketohexose. glucose fructose A more general classification scheme exists where carbohydrates are broken down into the groups monosaccharides, disaccharides, and polysaccharides. Monosaccharides are often referred to as simple sugars. These compounds cannot be broken down into smaller sugars by acid hydrolysis. Glucose, fructose and ribose are examples of monosaccharides. Monosaccharides exist mostly as cyclic structures containing hemiacetal or hemiketal groups. These structures in solution are in equilibrium with the corresponding open-chain structures bearing aldehyde or ketone functional groups. The chemical linkage of two monosaccharides forms disaccharides.
    [Show full text]
  • Nucleosides & Nucleotides
    Nucleosides & Nucleotides Biochemistry Fundamentals > Genetic Information > Genetic Information NUCLEOSIDE AND NUCLEOTIDES SUMMARY NUCLEOSIDES  • Comprise a sugar and a base NUCLEOTIDES  • Phosphorylated nucleosides (at least one phosphorus group) • Link in chains to form polymers called nucleic acids (i.e. DNA and RNA) N-BETA-GLYCOSIDIC BOND  • Links nitrogenous base to sugar in nucleotides and nucleosides • Purines: C1 of sugar bonds with N9 of base • Pyrimidines: C1 of sugar bonds with N1 of base PHOSPHOESTER BOND • Links C3 or C5 hydroxyl group of sugar to phosphate NITROGENOUS BASES  • Adenine • Guanine • Cytosine • Thymine (DNA) 1 / 8 • Uracil (RNA) NUCLEOSIDES • =sugar + base • Adenosine • Guanosine • Cytidine • Thymidine • Uridine NUCLEOTIDE MONOPHOSPHATES – ADD SUFFIX 'SYLATE' • = nucleoside + 1 phosphate group • Adenylate • Guanylate • Cytidylate • Thymidylate • Uridylate Add prefix 'deoxy' when the ribose is a deoxyribose: lacks a hydroxyl group at C2. • Thymine only exists in DNA (deoxy prefix unnecessary for this reason) • Uracil only exists in RNA NUCLEIC ACIDS (DNA AND RNA)  • Phosphodiester bonds: a phosphate group attached to C5 of one sugar bonds with - OH group on C3 of next sugar • Nucleotide monomers of nucleic acids exist as triphosphates • Nucleotide polymers (i.e. nucleic acids) are monophosphates • 5' end is free phosphate group attached to C5 • 3' end is free -OH group attached to C3 2 / 8 FULL-LENGTH TEXT • Here we will learn about learn about nucleoside and nucleotide structure, and how they create the backbones of nucleic acids (DNA and RNA). • Start a table, so we can address key features of nucleosides and nucleotides. • Denote that nucleosides comprise a sugar and a base.
    [Show full text]
  • 8| Nucleotides and Nucleic Acids
    8| Nucleotides and Nucleic Acids © 2013 W. H. Freeman and Company CHAPTER 8 Nucleotides and Nucleic Acids Key topics: – Biological function of nucleotides and nucleic acids – Structures of common nucleotides – Structure of double‐stranded DNA – Structures of ribonucleic acids – Denaturation and annealing of DNA – Chemistry of nucleic acids; mutagenesis Functions of Nucleotides and Nucleic Acids • Nucleotide Functions: – Energy for metabolism (ATP) – Enzyme cofactors (NAD+) –Signal transduction (cAMP) • Nucleic Acid Functions: – Storage of genetic info (DNA) – Transmission of genetic info (mRNA) –Processing of genetic information (ribozymes) –Protein synthesis (tRNA and rRNA) Nucleotides and Nucleosides • Nucleotide = – Nitrogeneous base –Pentose – Phosphate • Nucleoside = – Nitrogeneous base –Pentose • Nucleobase = – Nitrogeneous base Phosphate Group •Negatively charged at neutral pH • Typically attached to 5’ position – Nucleic acids are built using 5’‐triphosphates •ATP, GTP, TTP, CTP – Nucleic acids contain one phosphate moiety per nucleotide •May be attached to other positions Other Nucleotides: Monophosphate Group in Different Positions Pentose in Nucleotides • ‐D‐ribofuranose in RNA • ‐2’‐deoxy‐D‐ribofuranose in DNA •Different puckered conformations of the sugar ring are possible Nucleobases •Derivatives of pyrimidine or purine • Nitrogen‐containing heteroaromatic molecules •Planar or almost planar structures •Absorb UV light around 250–270 nm Pyrimidine Bases • Cytosine is found in both DNA and RNA •Thymineis found only in DNA
    [Show full text]
  • Nucleotides and Nucleic Acids
    CHAPTER 8 Nucleotides and Nucleic Acids Functions of Nucleotides and Nucleic Acids • Nucleotide Functions: – Energy for metabolism (ATP) – Enzyme cofactors (NAD+) – Signal transduction (cAMP) • Nucleic Acid Functions: – Storage of genetic info (DNA) – Transmission of genetic info (mRNA) – Processing of genetic information (ribozymes) – Protein synthesis (tRNA and rRNA) Nucleotides and Nucleosides • Nucleotide = – Nitrogeneous base – Pentose – Phosphate • Nucleoside = – Nitrogeneous base – Pentose • Nucleobase = – Nitrogeneous base Phosphate Group • Negatively charged at neutral pH • Typically attached to 5’ position – Nucleic acids are built using 5’- triphosphates • ATP, GTP, TTP, CTP – Nucleic acids contain one phosphate moiety per nucleotide • May be attached to other positions Other Nucleotides: Monophosphate Group in Different Positions Pentose in Nucleotides • -D-ribofuranose in RNA • -2’-deoxy-D-ribofuranose in DNA • Different puckered conformations of the sugar ring are possible Purine Bases • Adenine and guanine are found in both RNA and DNA • Also good H-bond donors and acceptors • Adenine pKa at N1 is 3.8 • Guanine pKa at N7 is 2.4 • Neutral molecules at pH 7 • Derivatives of pyrimidine or purine • Nitrogen-containing heteroaromatic molecules • Planar or almost planar structures • Absorb UV light around 250–270 nm Pyrimidine Bases • Cytosine is found in both DNA and RNA • Thymine is found only in DNA • Uracil is found only in RNA • All are good H-bond donors and acceptors • Cytosine pKa at N3 is 4.5 • Thymine pKa at N3 is 9.5
    [Show full text]
  • Carbohydrates: Disaccharides and Polysaccharides
    Carbohydrates: Disaccharides and Polysaccharides Disaccharides Linkage of the anomeric carbon of one monosaccharide to the OH of another monosaccharide via a condensation reaction. The bond is termed a glycosidic bond. The end of the disaccharide that contains the anomeric carbon is referred to as the reducing end because it is capable of reducing various metal ions. Formation of a glycosidic bond between two glucose molecules. Nomenclature: To describe disaccharides you need to specify the following: 1. The names of the two monosaccharides. 2. How they are linked together (one anomeric is always used). 3. The configuration of the anomeric carbons on both monosaccharides. The Six Simple Rules for Naming Disaccharides are as follows: 1. The non-reducing end defines the first sugar. 2. Configuration of the anomeric carbon of the 1st sugar (α,β). 3. Name of 1st monosaccharide, root name followed by pyranosyl (6- ring) or furanosyl (5-ring). 4. Atoms which are linked together, 1st sugar then 2nd sugar. 5. Configuration of the anomeric carbon of the second sugar (α,β) (often omitted if the anomeric carbon is free since α and β forms are in equilibrium.) 6. Name of 2nd monosaccharide, root name followed by pyranose (6- ring) or furanose (5-ring) (If both anomeric carbons are involved, then the name ends in ‘oside”, not ‘ose’) Example: Sucrose (table sugar): The anomeric carbon of glucose forms a bridge to the anomeric carbon of fructose. Since there is no reducing end, either sugar can be used to begin the name. Sucrose, drawn in two different ways. Note that both anomeric carbons are involved in the glycosidic linkage, thus both conformations have to be specified.
    [Show full text]
  • Structures and Characteristics of Carbohydrates in Diets Fed to Pigs: a Review Diego M
    Navarro et al. Journal of Animal Science and Biotechnology (2019) 10:39 https://doi.org/10.1186/s40104-019-0345-6 REVIEW Open Access Structures and characteristics of carbohydrates in diets fed to pigs: a review Diego M. D. L. Navarro1, Jerubella J. Abelilla1 and Hans H. Stein1,2* Abstract The current paper reviews the content and variation of fiber fractions in feed ingredients commonly used in swine diets. Carbohydrates serve as the main source of energy in diets fed to pigs. Carbohydrates may be classified according to their degree of polymerization: monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Digestible carbohydrates include sugars, digestible starch, and glycogen that may be digested by enzymes secreted in the gastrointestinal tract of the pig. Non-digestible carbohydrates, also known as fiber, may be fermented by microbial populations along the gastrointestinal tract to synthesize short-chain fatty acids that may be absorbed and metabolized by the pig. These non-digestible carbohydrates include two disaccharides, oligosaccharides, resistant starch, and non-starch polysaccharides. The concentration and structure of non-digestible carbohydrates in diets fed to pigs depend on the type of feed ingredients that are included in the mixed diet. Cellulose, arabinoxylans, and mixed linked β-(1,3) (1,4)-D-glucans are the main cell wall polysaccharides in cereal grains, but vary in proportion and structure depending on the grain and tissue within the grain. Cell walls of oilseeds, oilseed meals, and pulse crops contain cellulose, pectic polysaccharides, lignin, and xyloglucans. Pulse crops and legumes also contain significant quantities of galacto-oligosaccharides including raffinose, stachyose, and verbascose.
    [Show full text]
  • Impact of Glycosidic Bond Configuration on Short Chain Fatty
    nutrients Article Impact of Glycosidic Bond Configuration on Short Chain Fatty Acid Production from Model Fermentable Carbohydrates by the Human Gut Microbiota Hannah C. Harris 1,2, Christine A. Edwards 1 and Douglas J. Morrison 2,* 1 School of Medicine, Dentistry and Nursing, College of Medical Veterinary and Life Sciences, University of Glasgow, Glasgow G31 2ER, UK; [email protected] (H.C.H.); [email protected] (C.A.E.) 2 Scottish Universities Environmental Research Centre, University of Glasgow, Glasgow G75 0QF, UK * Correspondence: [email protected]; Tel.: +44-135-527-0134 Received: 17 October 2016; Accepted: 22 December 2016; Published: 1 January 2017 Abstract: Short chain fatty acids (SCFA) are the major products of carbohydrate fermentation by gut bacteria. Different carbohydrates are associated with characteristic SCFA profiles although the mechanisms are unclear. The individual SCFA profile may determine any resultant health benefits. Understanding determinants of individual SCFA production would enable substrate choice to be tailored for colonic SCFA manipulation. To test the hypothesis that the orientation and position of the glycosidic bond is a determinant of SCFA production profile, a miniaturized in vitro human colonic batch fermentation model was used to study a range of isomeric glucose disaccharides. Diglucose α(1-1) fermentation led to significantly higher butyrate production (p < 0.01) and a lower proportion of acetate (p < 0.01) compared with other α bonded diglucoses. Diglucose β(1-4) also led to significantly higher butyrate production (p < 0.05) and significantly increased the proportions of propionate and butyrate compared with diglucose α(1-4) (p < 0.05).
    [Show full text]
  • Chapter 6 Carbohydrates Outline 6.1 Classes of Carbohydrates 6.1
    2/25/2015 Outline Lecture Presentation • 6.1 Classes of Carbohydrates • 6.2 Functional Groups in Monosaccharides Chapter 6 • 6.3 Stereochemistry in Monosaccharides Carbohydrates • 6.4 Reactions of Monosaccharides • 6.5 Disaccharides • 6.6 Polysaccharides Julie Klare • 6.7 Carbohydrates and Blood Fortis College Smyrna, GA © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 6.1 Classes of Carbohydrates 6.1 Classes of Carbohydrates • The simplest carbohydrates are • Disaccharides consist of two monosaccharide monosaccharides (mono is Greek for “one,” units joined together. sakkhari is Greek for “sugar”). • A disaccharide can be split into two • These often sweet-tasting sugars cannot be monosaccharide units. Ordinary table sugar, broken down into smaller carbohydrates. sucrose, C12H22O11, is a disaccharide that can be broken up, through hydrolysis, into the • The common carbohydrate glucose, C6H12O6, is a monosaccharide. monosaccharides glucose and fructose. • Monosaccharides contain carbon, hydrogen, • Oligosaccharidesare carbohydrates and oxygen and have the general formula containing three to nine monosaccharide units. The blood-typing groups known as ABO are Cn(H2O)n, where n is a whole number 3 or higher. oligosaccharides. © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 6.1 Classes of Carbohydrates 6.1 Classes of Carbohydrates • When 10 or more monosaccharide units are joined together, the large molecules that result are polysaccharides (poly is Greek for “many”). • The sugar units can be connected in one continuous chain or the chain can be branched. • Starch, a polysaccharide in plants, contains branched chains of glucose that can be broken down to produce energy. © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. 1 2/25/2015 6.1 Classes of Carbohydrates 6.1 Classes of Carbohydrates FIBER IN YOUR DIET FIBER IN YOUR DIET • Dietary fibers are carbohydrates that we cannot digest • Insoluble fibers do not mix with water, although they with our own enzymes.
    [Show full text]
  • Twisting of Glycosidic Bonds by Hydrolases
    Carbohydrate Research 344 (2009) 2157–2166 Contents lists available at ScienceDirect Carbohydrate Research journal homepage: www.elsevier.com/locate/carres Twisting of glycosidic bonds by hydrolases Glenn P. Johnson a, , Luis Petersen b, , Alfred D. French a, Peter J. Reilly b,* a Southern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, 1100 Robert E. Lee Boulevard, New Orleans, LA 70124-4305, USA b Department of Chemical and Biological Engineering, 2114 Sweeney Hall, Iowa State University, Ames, IA 50011-2230, USA article info abstract Article history: Patterns of scissile bond twisting have been found in crystal structures of glycoside hydrolases (GHs) that Received 6 July 2009 are complexed with substrates and inhibitors. To estimate the increased potential energy in the sub- Received in revised form 7 August 2009 strates that results from this twisting, we have plotted torsion angles for the scissile bonds on hybrid Accepted 11 August 2009 Quantum Mechanics::Molecular Mechanics energy surfaces. Eight such maps were constructed, including Available online 14 August 2009 one for a-maltose and three for different forms of methyl a-acarviosinide to provide energies for twisting of a-(1,4) glycosidic bonds. Maps were also made for b-thiocellobiose and for three b-cellobiose conform- Keywords: ers having different glycon ring shapes to model distortions of b-(1,4) glycosidic bonds. Different GH fam- Conformational analysis ilies twist scissile glycosidic bonds differently, increasing their potential energies from 0.5 to 9.5 kcal/ Glycoside hydrolases Glycosidic bonds mol. In general, the direction of twisting of the glycosidic bond away from the conformation of lowest Intramolecular energy intramolecular energy correlates with the position (syn or anti) of the proton donor with respect to the Molecular mechanics glycon’s ring oxygen atom.
    [Show full text]
  • Science Sixtyseventh67 National Conference a Platform for Progress
    science sixtyseventh67 national conference a platform for progress 67th ASEV National Conference June 27–30, 2016 Portola Hotel & Monterey Marriott Monterey, California USA TECHNICAL ABSTRACTS american society for enology and viticulture june 27th – 30th, 2016 — monterey, california 45 2016 National Conference Technical Abstracts sixtyseventh67 national conference Oral Presentation Abstracts Wednesday, June 29 progress Enology — General .....................................................................................48–51 Viticulture — Disease Management ............................................................52–55 Viticulture — General .................................................................................56–59 a platform for science Thursday, June 30 Enology — Microbiology ............................................................................60–63 Enology — Phenolics .................................................................................64–67 Viticulture — Water Relations ....................................................................68–71 Enology — Sensory .....................................................................................72–74 Poster Presentation Abstracts Wednesday, June 29 & Thursday, June 30 Enology & Viticulture ...............................................................................75–118 Industry .................................................................................................119–123 NOTE: pp. 1-45 constituted the program section of the original
    [Show full text]
  • Glycogen Metabolism CH2OH CH2OH Glycogen H O H H O H H H OH H OH H 1 O OH O H OH H OH
    Glycogen Metabolism CH2OH CH2OH glycogen H O H H O H H H OH H OH H 1 O OH O H OH H OH CH2OH CH2OH 6 CH2 CH2OH CH2OH H O HH O H H 5 O H H O H H O H H H H H H 1 4 OH H OH H 4 OH H OH H OH H O O O O OH OH 3 2 H OH H OH H OH H OH H OH Glycogen is a polymer of glucose residues linked by (14) glycosidic bonds, mainly (16) glycosidic bonds, at branch points. Glycogen chains & branches are longer than shown. Glucose is stored as glycogen predominantly in liver and muscle cells. CH2OH H O H H OH H 2 Glycogen catabolism OH OPO3 H OH (breakdown): glucose-1-phosphate Glycogen Phosphorylase catalyzes phosphorolytic cleavage of the (14) glycosidic linkages of glycogen, releasing glucose‐1‐phosphate as reaction product. glycogen(n residues) +Pi glycogen (n–1 residues) +glucose‐1‐phosphate This phosphorolysis may be compared to hydrolysis: Hydrolysis: R-O-R' + HOH R-OH + R'-OH 2- 2- Phosphorolysis: R-O-R' + HO-PO3 R-OH + R'-O-PO3 Pyridoxal phosphate (PLP), H O O C a derivative of vitamin B , O H2 6 PC OH serves as prosthetic group O O for Glycogen N CH3 Phosphorylase. H pyridoxal phosphate (PLP) lysine Enz H (CH2)4 H N+ CCOO 3 N+ CH O HC H 2 O H2 P C O CH2 O O CH2 CH2 N CH3 H NH3 Enzyme (Lys)-PLP Schiff base Pyridoxal phosphate (PLP) is held at the active site by a Schiff base linkage, formed by reaction of the aldehyde of PLP with the ‐amino group of a lysine residue.
    [Show full text]