. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 1 Developmentof ComplexCurriculaforMolecularBionicsand InfobionicsProgramswithina consortial* framework** Consortiumleader PETER PAZMANY CATHOLIC UNIVERSITY Consortiummembers SEMMELWEIS UNIVERSITY, DIALOG CAMPUS PUBLISHER The Project has beenrealisedwiththesupportof theEuropean Union and has beenco-financedbytheEuropean SocialFund*** **Molekuláris bionika és Infobionika Szakok tananyagának komplex fejlesztése konzorciumi keretben ***A projekt az Európai Unió támogatásával, az Európai Szociális Alap társfinanszírozásával valósul meg. PETER PAZMANY CATHOLIC UNIVERSITY SEMMELWEIS UNIVERSITY dk_fejlec.gif INFOBLOKK ITK_logo_new_375_v1 . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2 BIOCHEMISTRY CATABOLISM OF CARBOHYDRATES www.se.hu (BIOKÉMIA) (A SZÉNHIDRÁTOK LEBONTÁSA) TRETTER LÁSZLÓ http://semmelweis-egyetem.hu/ Biochemistry: Catabolism of carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 3 www.se.hu http://semmelweis-egyetem.hu/ CatabolismDEF: Part of intermediary metabolism dealing with the energy-yielding degradation of nutrient molecules CarbohydratesDEF: Aldehyde or ketone derivatives of polyhydric alcohols Antonym of catabolism: anabolism Examples for catabolic processes Decomposition of glucose to pyruvate or lactate called: glycolysis Decomposition of fatty acids to acetyl-CoA called: beta oxidation Decomposition of glycogen to glucose: called glycogenolysis Decomposition of acetyl-CoA to carbon dioxide + water called: citric acid cycle Biochemistry: Catabolism of carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 4 www.se.hu http://semmelweis-egyetem.hu/ CLASSIFICATION of CARBOHYDRATES MonosacharidesDEF: those carbohydrates that cannot be hydrolyzed into a simpler form subdivision: trioses, tetroses, pentoses, hexoses, heptoses depending upon the number of carbon atom subdivision: aldoses or ketoses depending upon the presence of of aldehyde or ketone group DisaccharidesDEF: hydrolysis of disaccharides yields 2 molecules of monosaccharides OligosaccharidesDEF: Hydrolysis yields 3-6 monosaccharide units PolysaccharidesDEF: Hydrolysis yields more than 6 monosaccharide units Biochemistry: Catabolism of carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 5 www.se.hu http://semmelweis-egyetem.hu/ Examples for monosaccharides Aldoses Ketoses Trioses (C3H6O3) Glycerose Synonym: Glycer-aldehyde Dihydroxy-acetone Tetroses (C4H8O4) Erythrose Erythrulose Pentoses (C5H10O5) Ribose Ribulose Hexoses (C6H12O6) Glucose Galactose Mannose Fructose Biochemistry: Catabolism of carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 6 www.se.hu http://semmelweis-egyetem.hu/ Table of contents: Glycolysis, the anaerobic decomposition of glucose Catabolism of non-glucose carbohydrates Regulation of carbohydrate catabolism Biochemistry: Catabolism of carbohydratesGlycolysis . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 7 www.se.hu http://semmelweis-egyetem.hu/ Glycolysis -reactions Learning objectives: Carbohydrates are major energy giving substrates for a living organism Glycolysisan universal pathway to decompose glucose even in the absence of oxygen At the end of the presentation students will be able: 1. To reproduce the most important steps of glycolysis 2. To understand the formation of ATP in the absence of oxygen 3. To demonstrate important principles of thermodinamics using examples taken from glycolysis . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 8 www.se.hu http://semmelweis-egyetem.hu/ GlycolysisDEF - Anaerobic degradation of glucose to lactate or - Anaerobic degradation of glucose to pyruvate –a preparatory pathway for the aerobic metabolism of glucose - Can occur in every cell - Energy yielding pathway (2 ATP/glucose) In the absence of oxygen every cell would perform glycolysis and the end-product will be lactate thus glycolysis is the most universal metabolic pathway. Biochemistry: Catabolism of carbohydratesGlycolysis . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 9 www.se.hu http://semmelweis-egyetem.hu/ Glycolysis -reactions Overview of glycolysis Glucose C6 Hexose phosphates (C6) Triose phosphate Triose phosphate Pyruvate (C3) Lactate (C3) Lactate blood NADH+H+ NAD+ CO2 H2O ATP + O2 Without O2 or no mitochondria ATP formation Biochemistry: Catabolism of carbohydratesGlycolysis . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 10 www.se.hu http://semmelweis-egyetem.hu/ Overview of glycolysis In the absence of oxygen or mitochondria 2 NAD+ 2 NADH+H+ In the presence of oxygen and mitochondria Glycolysis -reactions Biochemistry: Catabolism of carbohydratesGlycolysis . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 11 www.se.hu http://semmelweis-egyetem.hu/ Glycolysis -reactions Preparatory phase of glycolysis 2 ATP invested and Hexose chain is converted into triose phosphates Biochemistry: Catabolism of carbohydratesGlycolysis . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 12 www.se.hu http://semmelweis-egyetem.hu/ ATP requiring reactions of glycolysis Hexokinase Glucokinase Phosphofructokinase-1 .G’o= -16.7 kJ/mol irreversible .G’o= -14.2 kJ/mol Irreversible Rate limiting step of glycolysis Important reactions of the preparatory phase Biochemistry: Catabolism of carbohydratesGlycolysis . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 13 www.se.hu http://semmelweis-egyetem.hu/ Important reactions of the preparatory phase Hexokinase and glucokinase are isoenzymes IsoenzymesDEF: Enzymes catalyzing the same reaction But differ: In amino acid sequence Vmax, and/or KM in regulation Hexokinases are localized in the peripheral tissues Glucokinase is localized in the liver Hexokinases show high affinity for glucose Glucokinase show low affinity for glucose Their regulation is different Biochemistry: Catabolism of carbohydratesGlycolysis . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 14 www.se.hu http://semmelweis-egyetem.hu/ Important reactions of the payoff phase .G’o= 6.3 kJ/mol reversible .G’o= -18.5 kJ/mol reversible .G’o= -31.4 kJ/mol irreversible Inorganic phosphate incorporation NADH formation High energy acyl-phosphate group formation on the 1stC atom The acyl-phosphate group is transferred to ADP Substrate level phosphorylation From the high energy enol-phosphate bond the phosphoryl group is transferred to ADP Substrate level phosphorylation Biochemistry: Catabolism of carbohydratesGlycolysis . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 15 www.se.hu http://semmelweis-egyetem.hu/ Energetic balance of glycolysis Preparatory phase 2 ATP invested -2 Payoff phase2x2 ATP produced (1 hexose 2 triose)+4 SummaryNet ATP production+2 Substrate level phosphorylationDEF: Formation of ATP by phosphoryl group transfer from a compound having high energy bound Examples for substrate level phosphorylation: in glycolysis: phosphoglycerate kinase reaction pyruvate kinase reaction in citric acid cycle: succinate thiokinase reaction Antonym of substrate level phosphorylation: oxidative phosphorylation Biochemistry: Catabolism of carbohydratesGlycolysis . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 16 www.se.hu http://semmelweis-egyetem.hu/ Glycolysis -Summary Glycolysis –the most important decomposition pathway of the most important carbohydrate -glycolysis produces energy even in the absence of oxygen -every higher eukaryotic cells are able to perform glycolysis -2 mol of ATP produced from 1 mol of glucose -in the presence of oxygen and mitochondria glycolysis is continued in the citric acid cycle -glycolysis has reversible and irreversible steps -the irreversible reactions of glycolysis are catalyzed by hexokinase (glucokinase in liver), phosphofructokinase and pyruvate kinase Biochemistry: Catabolism of carbohydratesGlycolysis Biochemistry: Catabolism of carbohydratesCatabolism of non-glucose carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 17 www.se.hu http://semmelweis-egyetem.hu/ Catabolism of non-glucose carbohydrates Introduction Carbohydrates are major energy giving substrates for living organism Besides glucose other carbohydrates (e.g. fructose and galactose) are also taken up by the organism, which sugars can be catabolized or can participate in the synthesis of other molecules Glycogen is a special storage form of glucose with a function in the maintenance of blood sugar level and in the energy supply of the muscle cells. . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 18 www.se.hu http://semmelweis-egyetem.hu/ Learning objectives At the end of the presentation students will be able: To understand the pathways used by individual carbohydrates to join to the mainstream of the metabolism To understand that consumption of different carbohydrates could change physiological pathways and could have pathological consequences as well. Biochemistry: Catabolism of carbohydratesCatabolism of non-glucose carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 19 www.se.hu http://semmelweis-egyetem.hu/ Fructose metabolism Availability of fructose: Natural sources: fruit juices, honey, disaccharide sucrose Food industry: High Fructose Corn Syrup Importance: Mainly changed to glucose in the liver and used in the body Pathological significance: hereditary fructose intolerance (fructose accumulation plus hypoglycemia), obesity Biochemistry: Catabolism of carbohydratesCatabolism of non-glucose carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 20 www.se.hu http://semmelweis-egyetem.hu/ Entry of fructose into glycolysis 1. In liver –major organ of fructose catabolism Glycolysis, gluconeogenesis Important:fructose catabolism in the liver bypasses phosphofructokinase-1! Biochemistry: Catabolism of carbohydratesCatabolism of non-glucose carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 21 www.se.hu http://semmelweis-egyetem.hu/ Entry of fructose into glycolysis 2. In skeletal muscle –less important in fructose catabolism Fructose Fructose 6-phosphate ATP ADP Hexokinase Glycolysis Hexokinase -not entirely specific for glucose -converts fructose to Fr 6-P at low [Glucose] at high [Fructose] Biochemistry: Catabolism of carbohydratesCatabolism of non-glucose carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 22 www.se.hu http://semmelweis-egyetem.hu/ Glycolysis, gluconeogenesis Pathological aspects of fructose metabolism X 1) Hereditary fructose intolerance Aldolase B deficiency [fr 1-P] increased Symptom: hypoglycemia Why? See:regulation of carbohydrate breakdown 2) High fructose consumption -Susceptibility to obesity,hyperlipidemia hyperlipidemiaDEF: increased concentration of lipids in the blood Biochemistry: Catabolism of carbohydratesCatabolism of non-glucose carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 23 www.se.hu http://semmelweis-egyetem.hu/ Galactose metabolism Availability of galactose: from milk sugar: lactose. Intestinal hydrolysis of lactose results in formation of galactose+glucose Galactose is metabolized mainly in the liver, can be converted to glucose Importance: needed for synthesis of glycoproteins, glycolipids, lactose (in lactating women) Pathological significance: galactosemia Lactose galactose + glucose Biochemistry: Catabolism of carbohydratesCatabolism of non-glucose carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 24 www.se.hu http://semmelweis-egyetem.hu/ Galactose metabolism Galactose galactokinase Galactose 1-phosphate UDP-Glc-Gal 1-P uridyltransferse Glucose 1-phosphate phosphoglucomutase Glucose 6-phosphate ATP ADP Glucose 1-P UDP-Glc pyrophosphorylase UDP-glucose UDP-galactose UTP PPi UDP-gal epimerease Biochemistry: Catabolism of carbohydratesCatabolism of non-glucose carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 25 www.se.hu http://semmelweis-egyetem.hu/ [Galactose] galactokinase [Galactose 1-phosphate] UDP-Glc-Gal 1-P uridyltransferse Glucose 1-phosphate phosphoglucomutase Glucose 6-phosphate ATP ADP Glucose 1-P UDP-Glc pyrophosphorylase UDP-glucose UDP-galactose UTP PPi UDP-gal epimerease Pathological aspects of galactose metabolism X Galactosemia: lack of UDP-Glc-Gal 1-P uridyltransferse Consequence: increased [Galactose] symptom: cataractDEF:opacity in the lens of the eye increased [Galactose 1-phosphate] symptoms: liver failure, mental retardation Biochemistry: Catabolism of carbohydratesCatabolism of non-glucose carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 26 www.se.hu http://semmelweis-egyetem.hu/ Glycogen metabolism Glycogen: the storage form of glucose in the body forms granules in the cytosol many cells contain glycogen the most important organs for storage: liver, skeletal muscle function of liver glycogen: maintenance of blood sugar level function of muscle glycogen: energetic support of contraction Structure: highly branched structure chains: alpha [1-4] glucosidic linkage branches: alpha [1-6] glucosidic linkage protein glycogenin is localized in the core of glycogen glycogenin is required for the synthesis molecular mass: in the order of millions Biochemistry: Catabolism of carbohydratesCatabolism of non-glucose carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 27 www.se.hu http://semmelweis-egyetem.hu/ The structure of glycogen 1 6 6 1 4 4 1 4 1 1 4 1 Glycogenin Biochemistry: Catabolism of carbohydratesCatabolism of non-glucose carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 28 www.se.hu http://semmelweis-egyetem.hu/ GlycogenolysisDEF: Intracellular decomposition of glycogen Resulting glucose in the liver and kidney cortex Resulting glucose 6-P in the muscle Synonym: glycogen breakdown Antonym: glycogenesis or glycogen synthesis The purpose of glycogenolysis in liver (and to a smaller extent in kidney cortex): maintenance of blood sugar level. Blood sugar level should be kept constant, because there are cells and tissues which gain energy exclusively from glucose The purpose of glycogenolysis in muscle cells: to support the energy requirement of contraction. Biochemistry: Catabolism of carbohydratesCatabolism of non-glucose carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 29 www.se.hu http://semmelweis-egyetem.hu/ The fate of glycogen-derived glucose after breakdown In liver: release to the bloodstream In muscle: glycolysis then citric acid cycle In muscle in shortage of oxygen: glycolysis ending with lactate production phosphoglucomutase Lactate dehydrogenase Pi Glycogen glycogen phosphorylase Glucose 1-P Glucose 6-P Pyruvate PDH complex Acetyl-CoA Citric acid cycle CO2+ H2O Glycolysis glucose 6-Pase Glucose Lactate Biochemistry: Catabolism of carbohydratesCatabolism of non-glucose carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 30 www.se.hu http://semmelweis-egyetem.hu/ Steps of glycogen breakdown 1 Glycogen Glycogen phosphorylase Debranching enzyme alpha (1›4) ›alpha (1›4) transferase activity Debranching enzyme Amylo (1›6)-glucosidase activity P Pi gl 1-P gl H2O Debranching enzyme has two catalytic activities Products of catabolism: shorter glycogen glucose 1-P glucose (captured by hexo-or glucokinase) Biochemistry: Catabolism of carbohydratesCatabolism of non-glucose carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 31 www.se.hu http://semmelweis-egyetem.hu/ Steps of glycogen breakdown 2 phosphoglucomutase glucose 6-phosphatase H2O Pi fructose 6-phosphate phosphohexose isomerase ER in liver Biochemistry: Catabolism of carbohydratesCatabolism of non-glucose carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 32 www.se.hu http://semmelweis-egyetem.hu/ Pathological aspects of glycogen breakdown Glycogen storage diseasesDEF:inherited disorders characterized by abnormal quantity or type of glycogen in tissues Examples: Name Deficiency Consequences Von Gierke’s disease Lack of glucose 6-phosphatase in liver and kidney Hypoglycemia, hyperlipemia Cori’s disease Lack of debranching enzyme Accumulation of abnormally branched glycogen Mc Ardle’s disesase Lack of glycogen phosphorylase in the skeletal muscle Diminished tolerance to exercise Biochemistry: Catabolism of carbohydratesCatabolism of non-glucose carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 33 www.se.hu http://semmelweis-egyetem.hu/ Summary: Catabolism of non-glucose carbohydrates were discussed Glycogen, fructose and galactose catabolism follows individual pathways All of the individual decomposition pathways will join to glycolysis, so the complete breakdown of these saccharides will be similar to that of glucose. Biochemistry: Catabolism of carbohydratesCatabolism of non-glucose carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 34 www.se.hu http://semmelweis-egyetem.hu/ Biochemistry: Catabolism of carbohydratesRegulation of carbohydrate catabolism Learning objectives At the end of the presentation students will be able: To understand the adaptation of carbohydrate catabolic pathways to the current requirement of the organism and the cell. To understand the concept that metabolic pathway can be regulated by different ways: the most important ones are: - Regulation by changing the gene expression - Regulation by reversible covalent modification (e.g. phosphorylation/dephosphorylation of the key enzymes - Regulation by allosteric effectors To understand that only a few of the enzymes are regulated in the metabolic pathways, usually the rate-limiting ones and those which catalyze irreversible reactions . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 35 www.se.hu http://semmelweis-egyetem.hu/ Biochemistry: Catabolism of carbohydratesRegulation of carbohydrate catabolism Multilevel regulation of glycolytic enzymes Gene expression Covalent modification Allosteric Enzyme Inducer repressor phosphorylation dephosphorylation activator inhibitor Hexokinase Gluc 6-P Glucokinase insulin Glucagon (cAMP) Starvation Fructose 1-P (through glucokinase regulatory protein) Fructose 6-P through glucokinase regulatory protein) Phosphofructokinase-1 insulin starvation Fructose 2,6-P2 AMP ATP, citrate, fatty acids Pyruvate kinase insulin Glucagon (cAMP) Starvation cAMP, Ca-CaM inactivation insulin Activation Fructose 1,6-P2 ATP, alanine . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 36 www.se.hu http://semmelweis-egyetem.hu/ Biochemistry: Catabolism of carbohydratesRegulation of carbohydrate catabolism Regulation of glucokinase (liver) Inative in the nucleus The regulation of glucokinase explains hypoglycemia detected in fructose intolerance. Accumulation of fructose 1-P suspends the regulatory protein-mediated inhibition of glucokinase, thus glycolysis will be accelerated Fructose 6-P mediated inhibition of glucokinase represents a negative fee back mechanism Accumulation In fructose intolerance . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 37 www.se.hu http://semmelweis-egyetem.hu/ Biochemistry: Catabolism of carbohydratesRegulation of carbohydrate catabolism Regulation of phosphofructokinase-1 in liver Insulin stimulates glycolysis Insulin + Phosphorylated: inactive Dephosphorylated: active . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 38 www.se.hu http://semmelweis-egyetem.hu/ Biochemistry: Catabolism of carbohydratesRegulation of carbohydrate catabolism Phosphorylated: inactive Glucagon + X X Regulation of phosphofructokinase-1 in liver Glucagon inhibits glycolysis . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 39 www.se.hu http://semmelweis-egyetem.hu/ Biochemistry: Catabolism of carbohydratesRegulation of carbohydrate catabolism Structure of 6-phosphofructo 2-kinase/fructose 2,6-bisphosphatase enzyme Tandem enzyme: one polypeptide chain –two catalytic activities Heart specific enzyme: Phosphorylation (PKA) of the phosphatase domain inactivates phosphatase activity Kinase activity will be dominant Glycolysis activated Liver specific enzyme: Phosphorylation (PKA) near the kinase domain inactivates kinase activity Phosphates activity will be dominant. Glycolysis is inactivated . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 40 www.se.hu http://semmelweis-egyetem.hu/ Biochemistry: Catabolism of carbohydratesRegulation of carbohydrate catabolism Allosteric regulation of glycolysis Meaning of regulators High [gluc 6-P] indicates that hexokinase activity is too high High [AMP] –indicates low energy charge of the cell (local regulator) High [ATP] –indicates high energy charge of the cell High [citrate] indicates the overflow of fatty acid synthesis precursors from the mitochondria to the cytosol Fructose 2,6-P2the most important regulator of the rate limiting step of glycolysis. The level of Fr 2,6-P2reflects hormonal changes. In liver insulin elevates [Fr 2,6-P2], glycolysis is stimulated Glucagon decreases [Fr 2,6-P2], glycolysis is inhibited Adrenalin decreases [Fr 2,6-P2], glycolysis is inhibited BUT! In the heart adrenaline elevates [Fr 2,6-P2], glycolysis is stimulated . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 41 www.se.hu http://semmelweis-egyetem.hu/ Biochemistry: Catabolism of carbohydratesRegulation of carbohydrate catabolism Regulation of glycogen breakdown cAMP level is elevated by some hormones cAMP activated protein kinase A phosphorylates and activates phosphorylase kinase Activated phosphorylase kinase phosphorylates and activates glycogen phosphorylase Activated glycogen phosphorylase catalyzes glycogen breakdown Those hormones which decrease cAMP level has opposite effect on glycogen breakdown Calciumactivates phosphorylase kinase. Activated phosphorylase kinase phosphorylates and activates glycogen phosphorylase, which catalyzes glycogen breakdown Glucose (in liver) inhibits glycogen phosphorylase, i.e. inhibits glycogenolysis AMP in muscle stimulates glycogen phosphorylase, i.e. activates glycogenolysis . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 42 www.se.hu http://semmelweis-egyetem.hu/ Biochemistry: Catabolism of carbohydratesRegulation of carbohydrate catabolism Summary: Carbohydrates are important sources of energy for the organisms. Glycolysis is a fundamental energy yielding metabolic pathway in every cell. The rate of glycolysis is strictly regulated by various mechanisms Changes of the gene expression of the most important enzymes are regulated by hormones and by the nutrition. Reversible chemical modification of the enzymes (phosphorylation/dephosphorylation) usually reflects hormonal influence. The level of allosteric modificators might reflect the actual changes in the local intracellular environment, but could be changed by hormonal effects as well (e.g. [fruc 2,6-P2] is dependent upon hormonal status). . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 43 www.se.hu http://semmelweis-egyetem.hu/ Biochemistry: Catabolism of carbohydratesRegulation of carbohydrate catabolism Recommended literature Orvosi Biokémia (Ed. Ádám Veronika) Biochemistry: Catabolism of carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 44 www.se.hu http://semmelweis-egyetem.hu/ Questions: Describe the regulation of fructose catabolism, compare it with the regulation of glucose catabolism Which are the irreversible steps of glycolysis? Which enzyme reaction is the rate-limiting enzyme in the glycolysis? How many ATP can be produced, if glycolysis starts from previously synthesized glycogen and ends up with lactate formation? What is the consequence of having different PFK2 isoenzymes in the heart and liver considering the effect of adrenaline on glycolysis? Biochemistry: Catabolism of carbohydrates . TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2011.09.13.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 45 www.se.hu http://semmelweis-egyetem.hu/ Questions: Which of the following statements are true for the PFK1? 1. The reaction catalized by the enzyme is irreversible in vivo 2. The activity of the enzyme can be inhibited by ATP 3. Its function is influenced by the ATP/ADP ratio 4. It is the fastest enzyme of the glycolysis 5. It works even in the absence of ATP A:2,3,5B:1,2,3C:1,2,3,4D:2,3,4,5E:1,3,4,5 Which of the following statements are true for the fructose metabolism? 1. Fructose is phosphorylated by hexokinase in the liver 2. Fructose metabolism does require a specific aldolase for Fr 1-P 3. Fructose can be converted to either pyruvate or glucose 4. Fructose consumption can not elevate the blood sugar level 5. Fructose catabolism in the liver bypasses phosphofructokinase A:2,3,5B:1,2,3C:1,2,3,4D:2,3,4,5E:1,3,4,5