Human diseases of carbohydrate metabolism Inherited enzyme deficiencies Mutations that change enzyme function or abolish enzyme activity Most are recessive since only one functional copy of gene is sufficient for needed activity Diabetes Lactose intolerance Galactosemia Glycogen storage disease

Monosaccharides - Aldoses # Isomers = 2 n where n = # of chiral carbons Epimers – differ in configuration at only one chiral carbon Enantiomer Distant chiral C From most oxidized Not all made in nature

Monosaccharides - Ketoses # Isomers = 2 n where n = # of chiral carbons

Cyclization - aldohexose Draw most oxidized carbon (C1 aldose and C2 ketose) on right and number C clockwise In ring most oxidizes carbon new chiral center (anomeric C) Transfer information from Fisher projections -OH on right then down in Haworth -OH on left then up in Haworth Bulky substituent on highest numbered carbon points up rapid equilibrium Anomers

Hemiacetal Cyclization - aldopentose Haworth projection Anomers Equilibrium Anomeric C

Glycolysis: Steps 2 and 3 Stereospecific: uses  -Glc; produces 100%  -D-fructose-6-phosphate Opens the chain during the rxn PFK-1 utilizes 100%  -anomer 36%  -fructose 64%  -fructose CH 2 OH OH

Glycoside Bonds – Disaccharides Hemiacetals -a reactive carbonyl that can be oxidized. reducing non-reducing non-reducing sugar No open chain equil  anomer: refers to free C 1 OH

Glycoside Bonds – Disaccharides epimer Most abundant disacc. in nature (plants)

Amylose Polysaccharides – Structure Humans don’t have  -glucosidases Microbe that live in ruminants do Plant cell walls, stems and branches ,000 Glc residues 180 deg rotation termites Rigid extended conformation H-bonding Forms bundles or fibrils Cellulose  -(1-4) linkage

Polysaccharides – Glucose Storage Amylose Amylopectin and Glycogen Plant starch – mixture of amylose and amylopectin Animals glycogen No template (ie no gene) Homoglycans- one type of monosaccharide glucose residues (maltose units) Amylopectin: branch every 25 residues Glycogen: branch every 8-12 residues 10% mass of liver

Polysaccharides -Starch Degradation Humans digest starch via two enzymes: – α -amylase - endoglycosidase of α-(1-4) linkages (random) – debranching enzyme (cleaves limit dextrans) Higher plants have – β- amylase exoglycosidase of α- (1-4) linkages, releasing the disaccharide maltose Single reducing end Know how starch is broken down ! multiple non-reducing end

Glycogen Metabolism Synthesis: Different enzymes for syn and degradation Driven by PPi hydrolysis Major regulatory step

Amylo-(1,4 1,6)-transglycolase catalyzes the branch point. (Alpha 1-6 link) (hormonally regulated) Pre-existing Glycogenin primer Key regulation by phosphorylation

Degradation: Phosphorolysis rxn. Generates phosph-sugar not free glc Two subunits, two catalytic sites, allosteric sites. AMP- activator; ATP & Glc-6-P – inhibitor. Phosphorylation: active (phosphorylase a). Dephosphorylated: less active (phosphorylase b). Primary regulation

Reg by ATP and G-6-P Primarily by phosphorylation phosphorolytic Consequences of branch Branching inc speed of syn and degradation Sequential removal of Glc From non-reducing end Stops 4 Glc from branch pt Energy yield from glycogen Higher than from glc Reducing vs non-reducing ends solubility Rate of syn/degradation

Human diseases of carbohydrate metabolism Inherited enzyme deficiencies Mutations that change enzyme function or abolish enzyme activity Most are recessive since only one functional copy of gene is sufficient for needed activity Diabetes Lactose intolerance Galactosemia Glycogen storage disease

α -amylase lactase Glc + Gal

Glc-6-P In liver Absorbed from intestine Major source of energy for nursing animals 20% of caloric intake of infants

Glucose metabolism Glc 6-P Glc Fruc 6-P Fruc 1,6-P Glc Glc 1-Pglucogen lactase Glc + Gal

Glc-6-P In liver Absorbed from intestine Major source of energy for nursing animals 20% of caloric intake of infants X X Two inherited metabolic errors Hypolactasia (lactose intolerance) Galactosemia

Lactose Intolerance Single gene defect X Normal decrease in enzyme by 6 yrs old 10% of original activity (Northern Europeans are lactase producing adults) Lactase deficient people: Bloated/ gas and diarrhea Can also hinder absorption of other nutrients bacteria in colon ferment to lactic acid, methane and H gas Lactose passes intact into colon Mutation in chromosome 2 Avoid dietary lactose Take enzyme substitute

cataracts X Galactosemia Galactose 1-P accumulates in liver cells (high galactose in blood and urine) Decrease liver function and cataracts death CNS damage and mental retardation (even if avoid milk) Cataracts (clouding) due to high galactose in eye. Converted to galactol allowing diffusion of water into eye

Glucose metabolism Glc 6-P Glc Fruc 6-P Fruc 1,6-P Glc Glc 1-Pglucogen

Glycolysis and Cancer Net Reaction: Glucose + 2 ADP + 2 NAD Pi  2 Pyruvate + 2 ATP + 2 NADH + 2 H H 2 O Defined: Glucose is converted anaerobically to the three carbon acid pyruvate Oxidative phosphorylation: allows more energy extracted from Glc Generates ATP at higher rate than Oxid Phosp Aerobic glycolysis: Warburg effect Otto Warburg-cancer cells utilize glycolysis even in presence of O2 Max energy when pyruvate from glycolysis enters Citric Acid Cycle Initial stages of tumor growth vessels grow at slower rate: cells deprived of O 2 Cells switch to reliance to glycolysis

Glycolysis and Cancer Can visualize tumors based on inc sugar uptake (PET scan) Continue to rely of Glycolysis even when O2 restored to tumor Treatment?? Blocking lactose dehydrogenase (block NAD regeneration turn off Glycolysis)

Glucose Glucose-6-phosphate Fructose-6-phosphate Fructose-1,6-bisphosphate Dihydroxyacetone phosphate Glyceraldehyde-3-phosphate 1,3-bisphosphoglycerate 3-phosphoglycerate 2-phosphoglycerate phosphoenolpyruvate pyruvate Glyceraldehyde-3-phosphate 1,3-bisphosphoglycerate 3-phosphoglycerate 2-phosphoglycerate phosphoenolpyruvate pyruvate Hexokinase Glucose-6-phosphate isomerase Phosphofructokinase-1 Trios phosphate isomerase Aldolase Glyceraldehyde-3-phosphate dehydrogenase Phosphoglycerate kinase Phosphoglycerate mutase Enolase Pyruvate kinase ATP ADP ATP ADP ATP ADP ATP ADP ATP ADP ATP NADH + H + NAD + + P i NADH + H + NAD + + P i H2OH2O H2OH2O Phosphorylation Substrate Level Phosphorylation Oxidation and Phosphorylation Isomerization Cleavage Isomerization Rearrangement Dehydration Know key reg steps!

Enzymatic Regulation of Glycolysis CAC intermediates, slow down, there is already adequate supply of energy Not moving forward, stop converting ATP Cellular rxns are converting ATP and ADP, make more ATP You’ve committed! Bi-phosphated furanoses, keep pathway moving

Glycolysis: Hexokinase Isozymes Can’t leave the cell with negative charge I-IIIIV Isozymes Different inhibition profiles Location, Km Control point Hexokinases (I-III) -regulated negatively by Glc-6-P -if later steps slow down, Glc-6P builds up Glucokinase (IV) in Liver -regulated negatively by Fru-6-P -pulls glucose out of bloodstream until equil -liver can produce more Glc-6-P -converts Glucose to Glycogen storage Glc 6-P Glc Fruc 6-P Fruc 1,6-P Glc Glc 1-Pglucogen

Insulin Dependent Uptake Muscle Adipose Hormones Involved High blood [Glc], insulin released Low blood [Glc], glucagon released in Liver Major function of liver: maintain constant level of Glc in blood Release Glc (from glycogen) during muscle activity and between meals

Most cases Glc-6-P is end product---used in other pathways - glycogen, starch, pentose, hexose synthesis Enzyme only found in liver, kidney, small intestines Bound to ER with active site towards lumen Hydrolysis of phosphate irreversibly forms glucose Secretory pathway exports to blood stream for other tissues Glucose 6-phosphatase

Lactate- produced in RBC and Muscle Cori cycle Lactate to pyruvate in liver Body does not transfer pyruvate Major function of liver: maintain constant level of Glc in blood Release Glc during muscle activity and between meals Breakdown of glycogen to Glc 6-P (does not leave the cell) Liver contains glc 6-phoshatase enzyme Glc not major fuel in liver

Regulation of Phosphofructokinase-1 Citrate - feedback inhibitor - regulates supply of pyruvate - links Glycolysis and CAC Fru-2,6-bisphosphate - strong activator - produced by PFK-2 when excess fru-6-phosphate - indirect means of substrate stimulation or feed forward activation ATP - product of pathway - allosteric inhibitor AMP - allosteric activator - relieves inhibition by ATP Large oligomeric enzyme bacteria/mammals - tetramer yeast - octamer

Regulation of Pyruvate Kinase High blood [Glc] Allosteric (feed-forward) activation Fructose-1,6-bisphosphate -allosterically activates -produced in step three -links control steps together + F 1,6 BP Inactivation by covalent modification -blood [Glc] drops, glucagon released -liver protein kinase A (PKA) turned on -PKA phosphorylates pyruvate kinase Allosteric inhibition by ATP -product of pathway and CAC Low blood [Glc]

Regulation of Glycogen Metabolism Hormonal Regulation: Via cAMP Via PIP 3 Fed state fasting Insulin: secreted by pancreas when Glc high inc rate of transport into cell and glycogen syn Glucagon: secreted when Glc low Epi: released by adrenal gland in response to neural signal (flight or flight) Sudden energy response GLUT4

glycogenPPP Glc also syn from pyruvate (lactate and amino acids) Liver/kidney Glc needed in brain/muscle Gluconeogenesis Liver - 3 places differ- control points in glycolysis - 4 new enzymes ATP energy, NADH reducing equivalents consumed

: Regulation Gluconeogenesis: Regulation Low [Glc]: glucagon increases protein kinase A (activates Fru-2,6-bisP phosphatase) lowering [Fru-2,6- bisP]. Activate Glc syn and Loss of glycolysis stim Modulate one enzyme and affect 2 opposing pathways Sensitive regulatory point

Regulation of Glycogen Metabolism Hormonal Regulation: Via cAMP Via PIP 3 Fed state fasting Insulin: secreted by pancreas when Glc high inc rate of transport into cell and glycogen syn Glucagon: secreted when Glc low Epi: released by adrenal gland in response to neural signal (flight or flight) Sudden energy response GLUT4

Intracellular Regulation of Glycogen Metabolism by Interconvertible Enzymes: Low [Glc] Simultaneous effect Low glc activate kinase and breakdown

High [Glc]

Human diseases of carbohydrate metabolism Inherited enzyme deficiencies Mutations that change enzyme function or abolish enzyme activity Most are recessive since only one functional copy of gene is sufficient for needed activity Diabetes Lactose intolerance Galactosemia Glycogen storage disease Understand how enzyme deficiency leads to accumulation of glycogen Other symptoms Treatment, if any

Glycogen storage disease Glc 6-P Glc Fruc 6-P Fruc 1,6-P Glc Glc 1-Pglucogen X X X X I IV V VII II, III, VI I Glucose-6-Phosphatase in liver (von Gierk’s disease): Liver enlargementhypoglycemia (low blood glc) when fasting Branching enzyme in organs (liver) (Andersen’t disease) Liver dysfunction and early death Glycogen phosphorylase in muscle (McArdle’s disease) Phosphofructokinase in muscle VII IV V Inability to exercise Muscle cramps with exercise All defects lead to glycogen accumulation Glycogen accumulation and

Glycogen storage disease Glucose-6-Phosphatase deficiency in liver (von Gierk’s disease): Glc not released into blood hypoglycemia (low blood glc) between meals infant in convulsions Type I: No response to Epinephrine or Glucagon Large amounts of glycogen in liver (G-6-P inhibits breakdown) Glc-6-P increases glycolysis inc lactate/pyruvate in blood (Lactic acidosis) Continuous feedings of cornstarch (intragastric feeding) Drug induced inhibition of Glc uptake by liver Surgical transplant of portal vein (normally intestine-liver) Glc to peripheral tissues before liver Liver enlargement Delayed puberty, short stature

Glycogen storage disease Type IV: Branching enzyme deficiency in organs (liver) (Andersen’s disease) Accumulate abnormal glycogen Failure to thrive----- death 2-5 yrs old Liver dysfunction Reduced solubility of glycogen Foreign body immune response?? Most severe disease

Glycogen storage disease Type V: Glycogen phosphorylase deficiency in muscle (McArdle’s disease) No breakdown of glycogen Exercise indices muscle cramps otherwise normal Effective utilization of muscle glycogen not essential to life Can’t provide fuel for glycolysis to keep up Demand for ATP Muscle cramps correlate with inc ADP Vasodialation-muscle now has access to Glc and fatty acids in blood NMR on forearm muscle