Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download • Glycolysis • Gluconeogenesis • Glycogen synthesis
Document related concepts
no text concepts found
Transcript
Carbohydrate Metabolism! Wichit Suthammarak – Department of Biochemistry, Faculty of Medicine Siriraj Hospital – Aug 1st and 4th, 2014! • Glycolysis • Gluconeogenesis • Glycogen synthesis • Glycogenolysis • Pentose phosphate pathway • Metabolism of other hexoses Carbohydrate Digestion! Digestive enzymes! Polysaccharides/complex carbohydrates Amylase Salivary glands Pancreas Oligosaccharides/dextrins Membrane-‐bound Microvilli Brush border Dextrinase Maltose Maltase 2 glucose Sucrose Sucrase 1 glucose 1 fructose Lactose Lactase 1 glucose 1 galactose ‘Disaccharidase’ Lactose Intolerance! Cause & Pathophysiology! Lactose Normal lactose digestion Lactose intolerance Lactose Lactose Glucose X Lactase Small Intestine lactase Galactose Bacteria 1 glucose 1 galactose Large Intestine gases, organic acid, osmotically active molecules Normal stools Lactase deficiency! • Primary lactase deficiency: genetic defect, การสร้าง lactase ลด Fermentation อาการ! ลงเมื่ออายุมากขึ้น, พบมากที่สุด! ปวดท้อง, ถ่ายเหลว, คลื่นไส้อาเจียนภาย • Secondary lactase deficiency: หลังจากรับประทานอาหารที่มี lactose acquired/transient เช่น small bowel injury, gastroenteritis, inflammatory bowel disease! เป็นปริมาณมาก เช่นนม! Absorption of Hexoses! Site: duodenum! Intestinal lumen Membrane Transporter! Enterocytes Blood Na+" • Presents at the apical membrane ! of enterocytes! • Co-transports Na+ and glucose/! galactose! Na+" Glucose" Galactose" SGLT1 Glucose" Galactose" Fructose" Fructose" SGLT1: sodium-‐glucose transporter GLUT2 GLUT5 GLUT5 • Transports fructose from the ! intestinal lumen into enterocytes! GLUT2 Glucose! Galactose! GLUT2 Glucose" Galactose" Fructose! Fructose" GLUT2 • At the basal membrane: ! transports glucose, galactose! and fructose from enterocytes ! into bloodstream! GLUT2 • Presents at the apical membrane during high luminal [hexoses]! • Transports glucose, galactose, and fructose! The liver is the first stop for the most nutrients absorbed from ! the digestive tract! Glucose Uptake at the Peripheral Tissues! Glucose transporter- GLUT! Glucose Outside plasma membrane Glucose transporter (GLUT) Cytosol Glucose Transport via glucose transporter (GLUT) • GLUT: transmembrane glycoprotein on the plasma membrane! • Facilitated passive transport (no ATP required, downhill, protein carrier)! • Conformational change! Glucose Transporter! Transporter Tissue(s) Role GLUT1 Ubiquitous Endothelial cells of the blood-‐brain barrier Basal glucose uptake (every cell) Transport glucose from blood to CSF GLUT2 Liver, pancreas, intesHne Remove of excess glucose from blood GLUT3 Neuron Basal glucose uptake (neurons) GLUT4 Muscle, fat, heart AcHvity increased by insulin GLUT5 IntesHne, tesHs, kidney, sperm Primarily fructose transport GLUT6 -‐ GLUT12 Others Currently being studied GLUT4! Insulin-responsive glucose transporter! GLUT4 • Myocytes, skeletal muscle, adipocytes! • Insulin-responsive GLUT! o Increases glucose ! uptake up to 15X! • Some SCL2A4 mutations have been found to be associated with diabetes mellitus (DM)! Regulation of glucose transport by insulin-‐responsive GLUT4 (Lehninger Principle of Biochemistry, 4th edition) Kinetics of Glucose Uptake via GLUT! Initial velocity of glucose entry, V0 (uM/min) Characteristic of GLUT1 vs GLUT2! Vmax Normal plasma ! [glucose]! = 80 - 110 mg/dl! (4.5 - 6 mM)! ½ Vmax Kt Extracellular [glucose] (mM) GLUT1 GLUT2 • Every tissue! • Enterocyte, hepatocyte, pancreatic islet! • Kt of glucose ≈ 1.5 mM! • Kt of glucose ≈ 66 mM! • Basal glucose uptake! • Control plasma glucose! Major Pathways of Glucose Utilizations! Extracellular matrix and cell wall polysaccharides Glycogen, starch synthesis of ! structural polymer! storage;! ‘Glycogen synthesis’! GLUCOSE! oxidation via ! ‘Pentose phosphate pathway’! Ribose 5-‐phosphate oxidation via ! ‘Glycolysis’! Pyruvate Glycolysiszc! Glycolysis: glykys (Greek); sweet + lysis; splitting Breakdown of glucose! A series of enzyme-catalyzed reactions (10 reactions)- glycolytic pathway! Glucose 2ADP + 2Pi 2NAD+ 2ATP + 2H2O 2NADH 2Pyruvate Final product: 2 molecules of 3-carbon compound; pyruvate! Glycolysis provides the largest flux of carbon in most cells! Glycolysis! Embden-Meyerhof-Parnas pathway! Preparatory Phase Glucose ADP Glucose-6-phosphate Phosphohexose isomerase Fructose-6-phosphate Phosphofructokinase-1 ATP ADP Fructose-1,6-phosphate Aldolase Glyceraldehyde-3-phosphate + Dihydroxyacetone phosphate Triosephosphate isomerase hexokinase/ glucokinase ATP Glyceraldehyde-3-phosphate (x2) 2Pi 2NAD G3P dehydrogenase + 2NADH + H 1,3-Bisphosphoglycerate (x2) 2ADP Phosphoglycerate kinase 2ATP Glucose 2ATP 2Pi 4ADP + 2NAD 4ATP 2NADH 2Pyruvate 3-Phosphoglycerate (x2) Net: 2ATP, 2NADH" Phosphoglycerate mutase 2-Phosphoglycerate (x2) Enolase H2O Phosphoenolpyruvate (x2) 2ADP Pyruvate kinase 2ATP Pyruvate (x2) Rate-determining Reaction! • Hexokinase/ glucokinase! • Phosphofructokinase! • Pyruvate kinase! Glycolysis! Flux through a metabolic pathway can be regulated in several ways! 1. Availability of substrate! • GLUT1 (Kt 1.5 mM) vs GLUT2 (Kt 66 mM)! • Insulin-responsive GLUT4! 2. Concentration of enzymes responsible for rate-limiting steps! Insulin stimulates the transcription of the genes that encode ! • Hexokinase! • Pyruvate kinase! • Phosphofructokinase-1! • PFK-2/FBPase-2! 3. Allosteric regulation of enzymes! • Allosteric activator/inhibitor! 4. Covalent modification of enzymes! • Phosphorylation! Glycolysis! Rate-determining reactions: hexokinase vs glucokinase! • Every tissue! Relative enzymatic activity (Vo/Vmax) Hexokinase • Km ≈ 0.1 mM! • G6P is an allosteric inhibitor! normal plasma [glucose] Glucokinase • Hepatocyte, β-cell! • Km ≈ 10 mM! • G6P does not inhibit glucokinase! 0 5 10 [Glucose] mM 15 20 Glycolysis! Rate-determining reactions: phosphofructokinase-1 (PFK-1)! ATP Fructose-6" +" ATP" phosphate" ADP, AMP Fructose-1,6" bisphosphate" PFK-‐1 citrate +" ADP" F26P Allosteric inhibitor: ATP, citrate! ATP เป็น product ของกระบวนการ glycolysis! Citrate เป็นสารตั้งต้นใน Krebs cycle! Allosteric activators: ADP, AMP, fructose-2,6-bisphosphate (F26P)! ADP, AMP ได้จากปฏิกิริยา ATP hydrolysis! F26P เปลี่ยนมาจาก F6P ซึ่งเป็น glycolytic intermediate! Glycolysis! Formation of fructose-2,6-bisphosphate (F26P)! ATP Fructose-6-phosphate (glycolytic intermediate) PFK-2 insulin ADP Pi glucagon FBPase-2 Fructose-2,6-bisphosphate H2O Insulin กระตุ้น phosphofructokinase-2 Glucagon กระตุ้น fructose bisphosphatase-2 (PFK-2) เป็นผลให้ F26P มีปริมาณเพิ่มขึ้น ทำให้ glycolysis ถูกกระตุ้น ! (ผ่านการทำงานของ PFK-1)! (FBPase-2) เป็นผลให้ F26P มีปริมาณลดลง ! ทำให้ glycolysis ถูกยับยั้ง (ผ่านการทำงานของ PFK-1)! Glycolysis! Rate-determining reactions: pyruvate kinase! Covalent modification (liver only) Allosteric control (all glycolytic tissues) glucagon ADP F16BP PEP PEP ATP PKA ADP P Pyruvate kinase (L) (inactive) F16BP PP H2O Pi Pyruvate kinase (L/M) ATP acetyl-CoA long-chain fatty acids ATP Pyruvate Pyruva carbox Pyruvate transamination Alanine PKA- protein kinase A! PP- phosphoprotein phosphatase! During fasting, glycolysis is inhibited in the liver (glucagon signal) but unaffected in the muscle ! Hormone: insulin (éF26P)! Low energy index: ADP, AMP ! Intermediate: F16P! Hormone: glucagon (êF26P)! High energy index: ATP acetyl-CoA, citrate, LCFA! Intermediate: G6P! Glucose + -‐ 2Pyruvate 2ATP, 2NADH Glycolysis! Other clinical significance- formation of 2,3BPG in RBC! 1,3-Bisphosphoglycerate (x2) Phosphoglycerate kinase Bisphosphoglycerate mutase 2ADP 2ATP 3-Phosphoglycerate (x2) 2Pi 2,3-Bisphosphoglycerate (x2) 2,3-Bisphosphoglycerate phosphatase 2,3-‐bisphophoglycerate (2,3-‐BPG) 2,3-BPG มีผลต่อการจับกับ O2 ของ hemoglobin (O2 affinity): มีมาก จับน้อย ปล่อยง่าย! [2,3-BPG] in normal RBC ≈ 5 mM! [2,3-BPG] > 5 mM (eg. pyruvate kinase deficiency)- O2 delivery ไปยัง peripheral tissue ! [2,3-BPG] < 5 mM (eg. hexokinase deficiency)- O2 delivery ไปยัง peripheral tissue! Glycolysis! Other clinical significance- fluoride can inhibit enolase! O Glyceraldehyde-3-phosphate (x2) 2Pi 2NAD G3P dehydrogenase + 2NADH + H 1,3-Bisphosphoglycerate (x2) P O CH 2 CH O P O CH 2 CH C O OH P Fluoride ion (F-)! 2+) (cofactor ของเอนไซม์)! Magnesium ion (Mg O P O CH 2 CH C Phosphoglycerate mutase HO Inorganic phosphate (Pi) ! O OH 2-Phosphoglycerate (x2) Dental carries (ฟันผุ)! Common pathogen: Streptococcus mutans! 2ATP 3-Phosphoglycerate (x2) H OH 2ADP Phosphoglycerate kinase C EnolaseO Mg2 F2 Pi- inhibitory complex! CH 2 CH O Enolase C O ทำให้ 2PG เข้าถึง active site ไม่ได้! P H2O O Phosphoenolpyruvate (x2) 2ADP Pyruvate kinase 2ATP CH 2 Pyruvate (x2) CH3 C C O O P O C O C O Metabolic Fate of Pyruvate! NADH must be reoxidized! Glucose NAD+ NAD+ 2 Ethanol + 2CO2 NADH Anaerobic condition Yeast 2 Lactate NADH 2 Pyruvate Anaerobic condition Vigoriously contracting muscle RBC NADH 4CO2 2 Acetyl-CoA Krebs cycle 4CO2 + 4H2O ETC Aerobic condition NAD+ Anaerobic Glycolysis! Lactic and ethanol fermentation! Skeletal muscle, RBC! O O C C NADH + H+ O O NAD+ C HO lactate dehydrogenase (LDH) CH3 O C H CH3 Pyruvate Lactate Baker yeast! O CH3 C O C O Pyruvate CO2 pyruvate decarboxylase O CH3 C H Acetaldehyde NADH NAD+ alcohol dehydrogenase OH CH3 C H H Ethanol Anaerobic Glycolysis! Energy harvesting efficiency! Lactic Fermentation + 2NAD 2NADH Glucose 2ADP Ethanol Fermentation + 2NADH 2NAD 2Pyruvate 2Lactate + 2NAD 2NADH Glucose 2Pyruvate 2ADP 2ATP ΔG’° = -196 kJ/mol of glucose ! Efficiency! =! 2ATP! 196 kJ/mol! + 2NADH 2NAD 2EtOH + 2CO 2 2ATP ΔG’° = -235 kJ/mol of glucose ! Efficiency! =! 2ATP! 235 kJ/mol! =! 2(30.5 kJ/mol)! 196 kJ/mol! =! 2(30.5 kJ/mol)! 235 kJ/mol! =! 32%! =! 26%! Anaerobic Glycolysis! Rapid energy extraction! Anaerobic glycolysis Aerobic glycolysis + OXPHOS • Ethanol fermentation (2 ATP) 26%! • Lactic fermentation (2 ATP) 32%! • Glucose + 6O2! 34% (ΔG’° = -2,840 kJ/mol, 32 ATP)! Glucose 2 Ethanol + 2CO2 NADH Anaerobic condition Yeast Glucose NAD+ NAD+ 6CO2 + 6H2O! 2 Lactate NADH 2 Pyruvate Anaerobic condition Vigoriously contracting muscle RBC 2 Pyruvate NADH 4CO2 Anaerobic glycolysis (2 ATP) ! สามารถเกิดได้เร็วกว่า ! aerobic glycolysis + OXPHOS (32 ATP) ! ถึง 100 เท่า! 2 Acetyl-CoA Krebs cycle 4CO2 + 4H2O ETC Aerobic condition NAD+ Anaerobic Glycolysis! Fast-twitch vs slow-twitch muscles fiber! Fast-‐twitch fiber (type II) Slow-‐twitch fiber (type I) Fast! Slow! Metabolism Mainly anaerobic glycolysis! OXPHOS dependent! Fatigability Quickly! Relatively more slowly! Pale (pinkish)! Red (hemes in cytochromes)! Spinners! Marathoners! Rate of contraction Muscle histology Sport type Slow-Twitch Muscle Fiber in PGC-1α Transgenic Mice! Lin, et al., Nature 2002 WT = wild-type mice! Tg = PGC-1α transgenic mice ! PGC-1α is a transcriptional co-activator which promotes mitochondrial biogenesis! Acetyl-CoA Formation! • Aerobic condition! • Pyruvate is transported into the mitochondrial matrix! • Enzyme: pyruvate dehydrogenase complex (PDH complex)! Pyruvate dehydrogenase complex &Multienzyme Complexes • Catalytic core & &E1: pyruvate dehydrogenase! & E2: dihydrolipoyl transacetylase! & E3: dihydrolipoyl dehydrogenase! • Regulatory subunits & &Pyruvate dehydrogenase kinase! & &Pyruvate dehydrogenase phosphatase! Acetyl-CoA Formation! PDH complex deficiency- Wernicke-Korsakoff syndrome! O O C O C CH3 CoA-SH TPP NADH lipoate FAD pyruvate dyhydrogenase complex (E1 + E2 + E3) Pyruvate PDH complex deficiency • • • • + NAD S-CoA O C CH3 + CO2 Acetyl-CoA Wernicke-‐Korsakoff syndrome Mutation- inborn error of metabolism! • Thiamine deficiency- chronic alcoholism! Pyruvate is converted into lactic acid! • Neurons- OXPHOS dependent! Metabolic acidosis, coma, death! • Wernicke encephalopathy + ! Treatment! Korsakoff psychosis! § Ketogenic diet (fat > protein > CHO)! § Thiamine (B1), dichloroacetate! Acetyl-CoA Formation! PDH complex deficiency- Wernicke-Korsakoff syndrome! Thiamine pyrophosphate (TPP) Thiamine deficiency "Chronic alcoholism "Malnutrition, malaborption! &Liver- loss ability to store B1! Brain (neurons)-‐ mainly aerobic glycolysis + OXPHOS Shrinkage of the cerebral cortex ! and atrophy of basal forebrain regions! Wernicke encephalopathy Confusion! Loss of muscle coordination! Vision changes! Korsakoff psychosis Amnesia! Confabulation! Hallucination! Regulation of the PHD complex! Product inhibition! To control ‘carbon flux’ (acetyl unit) that enters the Krebs’ cycle ! FAD NAD+ [NADH]! [NAD+]! SH NADH+H SH CO2 O CH3 C O C Pyruvate O OH S CH3 C TPP HydroxyethylTPP S pyruvate dehydrogenase (E1) dihydrolipoyl dehydrogenase (E3) FAD R Lipoamide S S HS dihydrolipoyl HS transacetylase (E2) R O O TPP CH3 C S HS R Acetyl-dihydrolipoamide CH3 C S CoA Acetyl-CoA CoA [acetyl-CoA]! [CoA]! + Regulation of the PHD complex! Covalent modification! P Pyruvate dehydrogenase complex (inactive) ADP ADP CoA NAD+ Pyruvate 2+ PDK ATP Acetyl-CoA NADH ATP [NADH]! [NAD+]! H2O [acetyl-CoA]! [ATP]! [ADP]! [CoA]! PDP Pyruvate dehydrogenase complex (active) Ca 2+ Mg Pi Phosphorylation at E1 ! PDH complex ! is inhibited! Regulation of the PHD complex! Summary! 1) Product inhibition E2 (dihydrolipoyl transacetylase) is inhibited by! [acetyl-CoA]! [CoA]! E3 (dihydrolipoyl dehydrogenase) is inhibited by increased ! [NADH]! [NAD+]! 2) Covalent modification-‐ phosphorylation of E1 E1- (pyruvate dehydrogenase) is inactive when phosphorylated! PDK- activated by ATP, acetyl-CoA, NADH ! PDP- activated by Ca2+ and Mg2+! The Krebs Cycle! Glucose! Glycolysis 2 Pyruvate! PDH complex 2 Acetyl-CoA! 6 NADH! 2 FADH2! 2 GTP (ATP)! Krebs cycle Oxidative Phosphorylation (OXOHOS)! 1 NADH! 1 FADH2! ETC" 2.5 ATP! 1.5 ATP! ATP from Complete Oxidation of Glucose! Gluconeogenesis! Gluco; glucose, neo; new, genesis; synthesis" Gluconeogenesis: a metabolic pathway that regenerates glucose form ! & & & non-carbohydrate carbon substrates ! Pyruvate Lactate Glucose Glycerol Glucogenic amino acid Gluconeogenesis! Glucose ATP Glycolysis hexokinase/ glucokinase Pi glucose-6phosphatase Glucose-6-phosphate ADP Gluconeogenesis H2O phosphogluco isomerase Fructose-6-phosphate ATP Pi FBPase-1 PFK-1 ADP Fructose-1,6-bisphosphate H2O aldolase G3P triosephosphate isomerase 2NAD+ + 2Pi G3PDH 2NADH 2NAD+ + 2Pi DHAP 2NADH 1,3-Bisphosphoglycerate (x2) 2ADP 2ADP 2ATP 2ATP PGK 3-Phosphoglycerate (x2) phosphoglycerate mutase 2-Phosphoglycerate (x2) enolase 2ADP Phosphoenolpyruvate (x2) pyruvate kinase 2ATP 2GDP Pyruvate (x2) PEP carboxykinase 2GTP Oxaloacetate (x2) 2ADP 2ATP pyruvate carboxylase Gluconeogenesis! Hydrolysis of G6P by glucose-6-phosphatase in the ER! • An active site of glucose-6-phosphatase faces towards the ER lumen! • Separation of gluconeogenesis and glycogenolysis from glycolysis! • Plays a key role in homeostatic regulation of blood sugar levels! Gluconeogenesis! Cori cycle- synthesis of glucose from lactate! Liver Muscle blood glucose Glucose Glucose ADP + Pi NAD+ NAD+ ADP + Pi ATP NADH NADH ATP 2Pyruvate NADH NAD+ 2Pyruvate lactate dehydrogenase lactate dehydrogenase 2Lactate blood lactate NADH NAD+ 2Lactate Sources of lactate ! • Red blood cell! • Fast-twitch muscle fiber! Gluconeogenesis! Synthesis of glucose from glycerol! Fat mobilization • Shortage of liver glycogen (long starvation)! • Glycerol kinase! o Primarily expressed in liver! • Dihydroxyacetone phosphate (DHAP) is! used to synthesize glucose in order to! maintain blood glucose levels ! Gluconeogenesis! Synthesis of glucose from glucogenic amino acids! Protein mobilization Gluconeogenesis Oxaloacetate • Most dietary amino acid! • Structural protein (muscle protein) is the last source of The Krebs Cycle material for gluconeogenesis (after glycogen and fat)! • Glucogenic amino acids! Gluconeogenesis! Glucose-alanine cycle! Ammonia (NH4+) • Toxic product from protein degradation! • Glutamate transfers ammonia to pyruvate! Alanine • Transport ammonia from muscle to the liver! Glycolysis vs Gluconeogenesis! Futile cycle- uneconomical process! Glycolysis Gluconeogenesis Glucose Glucose 4ADP + 2GDP 6Pi 2NAD+ 2ADP + 2Pi 2NAD+ 2ATP + 2H2O 4ATP + 2GTP 6H2O 2NADH 2Pyruvate Net reaction:!2ATP + 2GTP + 4H2O 2NADH 2Pyruvate 2ADP + 2GDP + 2Pi! Coordinated Regulation of Glycolysis & Gluconeogenesis! Coordinated Regulation of Glycolysis & Gluconeogenesis! Gene expression control- hexokinase/glucose-6-phosphatase! Increased gene expression of the enzymes in the pathways! • High energy demand! o low [ATP]! • A need to increase production of glucose! o high [AMP]! o low blood [glucose]! o vigorous muscle contraction! o glucagon signaling! • Greater glucose consumption! o high blood [glucose]! o insulin signaling! Hexokinase Glucose-‐6-‐phosphatase Coordinated Regulation of Glycolysis & Gluconeogenesis! Allosteric control- PFK-1/FBPase-1! Gluconeogenesis ATP Fructose-6-phosphate Pi ATP ADP PFK-1 FBPase-1 AMP citrate F26F ADP H2O Fructose-1,6-bisphosphate Glycolysis High energy utilization ! • ATP hydrolysis: [ADP] and [AMP]! Low energy utilization! • ATP hydrolysis: [ATP]! • OXPHOS slows down: [citrate]! ATP Fructose-6-phosphate (glycolytic intermediate) PFK-2 insulin ADP Pi glucagon FBPase-2 Fructose-2,6-bisphosphate H2O Coordinated Regulation of Glycolysis & Gluconeogenesis! Mixed mechanism- pyruvate kinase/pyruvate carboxylase! Covalent modification (liver only) Allosteric control (all glycolytic tissues) glucagon ADP F16BP PEP PEP ATP PKA ADP P Pyruvate kinase (L) (inactive) F16BP PP H2O Pi Pyruvate kinase (L/M) ATP acetyl-CoA long-chain fatty acids ATP Pyruvate transamination Alanine Pyruvate carboxylase Pyruvate Coordinated Regulation of Glycolysis & Gluconeogenesis! Acetyl-CoA- antagonistic effect on glucose metabolism! Glucose Gluconeogenesis Oxaloacetate pyruvate carboxylase Pyruvate Glycolysis pyruvate kinase pyruvate DH complex Acetyl-CoA Kerbs cycle Energy Glucose Coordinated Regulation of Glycolysis & Gluconeogenesis! Summary! Hexokinase/glucose-‐6-‐phosphatase • Alteration in gene expression! • Insulin, glucagon and other signals that reflect cellular energy requirement ! PFK-‐1/FBPase-‐1 • Alloteric control! • ATP, ADP, AMP, citrate, F26P! • Insulin and glucagon influence the formation of F26P Pyruvate kinase/pyruvate carboxylase • Allosteric control and covalent modification! • Acetyl-CoA! Glycogen! Structure of Glycogen • Polymers of glucose ! • α(1 4) glycosidic (linked) and α(1 6) glycosidic bonds (branched)! • Cytosolic granules (β-particle) ! Function of Glycogen • Endogenous major storage reserve of glucose! o Muscle glycogen (1-2% of FW) ! ² & Important fuel during prolonged strenuous exercise (4-6 hr)! o Liver glycogen (10% of FW)! ² & Regulate plasma glucose (8-10 hr)! • Regulate osmotic pressure inside the cell ! o 10% of FW of the liver: 40,000x reduce in osmotic pressure ! Glycogen Synthesis! A starting point of a glycogen chain- glycogenin! Glycogenin OH + H HO Tyr 194 OH H H glucosyl transferase (intrinsic activity of glycogenin) Glycogenin Glycogenin CH2OH O H H UDP O OH UDP-glucose UDP + H HO Tyr 194 glucosyl transferase (x7 more times) (chain extending) CH2OH O H H OH H H O OH UDP-glucose UDP Glycogenin Tyr 194 Glycogen primer UDP Liver, muscle! Glycogen Synthesis! Elongation- glycogen synthase**! CH2 OH O H H H 4 OH H 1 HO O UDP CH2 OH CH2 OH O H O H H H H H 4 1 4 1 OH H OH H HO O O + H OH UDP-glucose H OH H OH Nonreducing end of a glycogen chain (glucose residue > 4) UDP glycogen synthase CH2 OH CH2 OH CH2 OH O H O H O H H H New H H H H 1 4 1 4 1 nonreducing 4 H OH H OH OH H end HO O O O H OH H OH H OH Elongated glycogen Glycogen synthase activated by G6P, insulin (after meal)! inhibited by glucagon, epinephrine (during meal, sympathetic) ! Glycogen Synthesis! Branching- glycogen-branching enzyme! Glycogen core glycogen-branching enzyme point Glycogen core • branching- a glycogen chain has at least 11 glucose residues! • transfer of 6-7 glucose residues from the nonreducing end to an interior position! Glycogen Synthesis! Summary! • Start! ü Glycogenin! ü Glucosyl transferase (intrinsic activity of glycogenin)! ü Glycogenin + 8 glucose residues = glycogen primer! • Elongation! ü Nonreducing end + UDP-glucose! ü Glycogen synthase***! • Branching ! ü Transfer of a terminal fragment of 6-7 glucose residues ! from nonreducing end! ü Forming α(1 6) glycosidic bond! ü Glycogen-branching enzyme! Glycogenolysis! Step 1- glycogen phosphorylase**! Nonreducing ends Glycogen glycogen phosphorylase P P P P P P Glycogen phosphorylase activated by glucagon, epinephrine, Ca2+! inhibited by insulin, glucose! Glycogenolysis! Step 2- glycogen debranching enzyme! glycogen debranching enzyme Glucose Unbranched glycogen ( Oligo α(1 6) to α(1 4) glucan-transferase! α(1 6) glucosidase ! Glycogenolysis! Step 3- phosphoglucomutase, glucose-6-phosphatase (liver only)! O O P O P O O P P O P P Glucose-1-phosphate phophoglucomutase P O P P O O P P O O P O Glucose-6-phosphate Muscle glucose-6-phosphatase Pi Glycolysis Free glucose GLUT2 Plasma glucose Liver Glycogenolysis! Summary! • Glycogen phosphorylase***! ü Removes the terminal glucose residue of a glycogen chain as G1P! ü Rate-limiting step of glycogenolysis! • Glycogen debranching enzyme! ü Oligo α(1 6) to α(1 4) glucan-transferase! ü α(1 6) glucosidase, resulting in a free glucose! • Phosphoglucomutase/ glucose-6-phosphatase (liver only)! ü Muscle: G1P G6P glycolysis! ü Liver: G1P G6P free glucose blood! Control of Glycogen Metabolism! Allosteric control! Glycogen synthase a (active) Glycogen phosphorylase b (inactive) AMP ATP G6P Glucose Glycogen phosphorylase a (active) Glycogen synthase b (inactive) Glycogen phosphorylase (liver):! ‘glucose sensor’! Glycogen synthase:! ‘G6P sensor’! Glycogenolysis Glycogen synthesis Control of Glycogen Metabolism! Hormonal control- glycogen phosphorylase! Glycogen phosphorylase b (inactive) phosphorylase a phosphatase P 2Pi 2ATP 2H2O 2ADP Glycogen phosphorylase a (active) glucagon (liver) phosphorylase b kinase epinephrine, Ca2+ (muscle) P Control of Glycogen Metabolism! Hormonal control: glycogen synthase! Insulin 3ADP 3ATP GSK3 P Glycogen synthase b (inactive) P Glycogen synthase a (active) P phosphorylase a phosphatase 3Pi Insulin Glucogan (liver) Ephinephrine (muscle) Control of Glycogen Metabolism! Summary! To increase plasma glucose To decrease plasma glucose ✓ Glycogenolysis! ✗ Glycogenolysis! ✗ Glycogen synthesis! ✓ Glycogen synthesis! + Glycogen phosphorylase:" -‐ + Glycogen synthase" glucagon, epinephrine! insulin! AMP, Ca2+! G6P! Glycogen synthase" glucagon, epinephrine! -‐ Glycogen phosphorylase" insulin, glucagon! glucose, ATP! Hyperglycemia: high plasma [glucose]! • Fasting hyperglycemia (at least 8 hours after meal)! plasma [glucose] > 130 mg/dl! • Postprandial hyperglycemia (2 hours after meals)! plasma [glucose] > 180 mg/dl! อาการของ hyperglycemia! • Temporary hyperglycemia- asymptomatic! • Chronic hyperglycemia- diabetes mellitus! Polyphagia, polydipsia, polyuria! Macrovascular and microvascular complications! NORMAL plasma [glucose] = 80 - 110 mg/dL ! Hypoglycemia: low plasma [glucose]! Plasma [glucose] < 60 mg/dl หรือตำ่จนมีอาการ! ..Metabolic emergency.. อาการของ hypoglycemia! Adrenergic manifestation: palpitating, sweating, tachycardia ! Glucagon manifestation: hunger, nausea, vomiting, headache! Neuroglycopenia: impaired judgment, confusion, seizure, coma! NORMAL plasma [glucose] = 80 - 110 mg/dL ! Plasma [glucose] mg/dL Glycolysis! 350 Gluconeogenesis! Glycogen synthesis! 300 Glycogenolysis! 250 200 150 100 Normal 50 0 0 1 2 3 4 5 6 Hours Plasma [glucose] mg/dL 350 300 250 DM" 200 150 100 Normal 50 0 0 1 2 3 4 5 6 Hours Diabetes mellitus! A defining characteristic of DM is chronic hyperglycemia! Plasma [glucose] mg/dL Cause Inability to lower blood glucose! 350 300 250 DM Classic symptoms Polydipsia, polyphagia, polyuria! 200 150 100 Normal 50 0 0 1 2 3 4 5 6 Hours Diabetes mellitus! World major metabolic disease! WHO- 346 million people worldwide (August 2011)! Diabetes mellitus! Type 1 DM! β-cells are destroyed! Diabetes mellitus! Type 2 DM! Genetic factor! • มีความผิดปกติของ gene ทำให้การ! ตอบสนองของเซลล์ต่อ insulin ลดลง! Environment! • Sedentary lifestyle (ไม่ออกกำลังกาย)! Genetic + Environment! • Too much fat/sugar intake! Diabetes mellitus! Main symptoms! Pentose Phosphate Pathway! Overview! Nonoxidative phase Oxidative phase Glucose-6-phosphate + NADP 2GSH glutathione reductase NADPH 6-Phosphogluconate + transketolase, transaldolase NADP CO2 NADPH Ribulose-5-phosphate Ribose-5-phosphate Nucleotides, coenzymes, DNA, RNA GSSG Fatty acids, sterols, etc. reductive biosynthesis Precussors Pentose Phosphate Pathway! Role of PPP! Ribose-‐5-‐phosphate and NADPH &Nucleic acid synthesis! &Rapidly dividing cells: bone marrow, skin, intestinal mucosa ! NADPH Reductive biosynthesis: fatty acids, steroid hormones, neurotransmitters! Fat tissue, liver, lactating mammary glands, adrenal gland, testis/ovaries! &Potent antioxidant: recycle GSH! Pentose Phosphate Pathway! Control of PPP: G6P is partitioned between glycolysis and PPP! Glucose Glycolysis Glucose-6-phosphate + NADP G6PD NADPH 6-Phosphogluconate + NADP CO2 NADPH Ribulose-5-phosphate 2GSH glutathione reductase GSSG Fatty acids, sterols, etc. reductive biosynthesis Precussors Ribose-5-phosphate NADP+ is an allosteric activator of G6PD! Pentose Phosphate Pathway! G6PD deficiency- epidemiology! • Most common enzyme defect! • Affected > 400 million people worldwide (2008)! • Distribution of G6PD deficiency resembles that of malaria ! Glucose-6-phosphate glucose-6-phosphate dehydrogenase NADP + NADPH 6-phosphoglucono lactonase 6-Phosphogluconate phosphogluconate dehydrogenase CO2 NADP + NADPH Ribulose-5-phosphate phosphopentose isomerase Ribose-5-phosphate M a l a r i a l B a n d Pentose Phosphate Pathway! G6PD deficiency: genetic defects! X-linked recessive! Most are missense mutations! Pentose Phosphate Pathway! G6PD deficiency: clinical manifestation! • Most G6PD-deficient individuals are asymptomatic! • Severe infection, some drugs, fava beans induce acute hemolysis ! Jaundice Dark urine • Deposition of bilirubin! • Hemoglobinuria! Pentose Phosphate Pathway! G6PD deficiency: molecular mechanism of acute hemolysis! Molecular oxygen Oxidative stress fava beans infection some drugs O2 e . Superoxide anion Induce oxidative damage to hemoglobin and RBC membrane (lipid peroxidation), resulting in HEMOLYSIS O2 2H + e GPx or catalase Hydrogen peroxide H2O2 2H + H2O Hydroxyl radical e 2GSH H2O GSSG . OH GR NADP Glucose 6-phosphate + NADPH 6-phospho- G6PD Metabolism of Hexoses other than Glucose! Fructose metabolism! Fructose ATP Muscle fructokinase ATP ADP fructose-1phosphate aldolase hexokinase ADP Fructose-6phosphate NADH NAD+ ATP ADP GAP GLYCOLYSIS Liver Fructose-1phosphate Glyceraldehyde alcohol DH glyceraldehyde kinase glycerol kinase + triosephosphate isomerase DHAP Glycerol glycerol phosphate DH NAD+ NADH GAP ATP ADP Metabolism of Hexoses other than Glucose! Defect in fructose metabolism: hepatic fructokinase deficiency! Fructose fructokinase ATP Fructose-1phosphate ADP (essential fructosuria) Rare genetic disorder, mutations in KHK gene Mode of inheritance: autosomal recessive Defect: liver cannot convert fructose to F1P Finding: fructosuria Sign and symptom: benign, mostly, asymptomatic Liver Metabolism of Hexoses other than Glucose! Defect in fructose metabolism: hereditary fructose intolerance! Fructose fructokinase ATP ADP Fructose-1phosphate Liver fructose-1phosphate aldolase Glyceraldehyde + DHAP Hereditary fructose intolerance Severe form of defect in fructose metabolism, ALDOB gene Mode of inheritance: autosomal recessive Defect: liver cannot metabolize F1P Finding: accumulation of F1P, liver damage Treatment: avoid fructose and sucrose Metabolism of Hexoses other than Glucose! Galactose metabolism! CH2 OH ATP ADP O H HO H OH H Galactokinase H OH H OH Galactose CH2 OH O H HO H OH H 2OPO3 H H OH Galactose-1-phosphate CH2 OH O H H H OH H HO O H OH UDP-Glucose O O P O P O O O Galactose-1-phosphate uridylyl transferase CH2 OH O H H H OH H 2HO OPO3 H OH Glucose-1-phosphate CH2 OH O H HO H OH H O H H OH UDP-Galactose Uridine UDP-galactose4-epimerase O O P O O P O O Uridine Metabolism of Hexoses other than Glucose! Defect in galactose metabolism: galactosemia! CH2 OH ATP ADP O H HO H OH H Galactokinase H OH H OH Galactose CH2 OH O H HO H OH H 2OPO3 H H OH Galactose-1-phosphate CH2 OH O H H H OH H HO O H OH UDP-Glucose O O P O P O O O Galactose-1-phosphate uridylyl transferase CH2 OH O H H H OH H 2HO OPO3 H OH Glucose-1-phosphate CH2 OH O H HO H OH H O H H OH UDP-Galactose Uridine UDP-galactose4-epimerase O O P O O P O Uridine O Galactosemia • most cases are caused by defect in galactose-1-phosphate uridylyl ! transferase deficiency (genetics)! • failure to thrive, mental retardation, death from liver damage! Metabolism of Hexoses other than Glucose! Galactosemic cataract! CH2 OH ATP ADP O H HO H OH H Galactokinase H OH H OH Galactose CH2 OH O H HO H OH H 2OPO3 H H OH Galactose-1-phosphate Galactosemia • galactose-1-phosphate is an allosteric inhibitor of galactokinase! • galactose can be reduced to galactitol! • accumulation of galactitol in the lens of the eye causes cataract! (ต้อกระจก)! CH2OH H C OH HO C H HO C H H C OH CH2OH Galactitol Metabolism of Alcohol! Consequences of Excessive Alcohol Consumption • alcohol induced hypoglycemia! • fatty liver! • liver cirrhosis!
Related documents