Glucose metabolism Processes –Glycolysis –Glycogenolysis –Gluconeogenesis Substrate level regulation Hormone level regulation

Carbohydrate metabolism Glycolysis –Breakdown of glucose to pyruvate –Provides substrate for TCA cycle Gluco-/glyco-neogenesis –Synthesis of glucose or glycogen –Storage of excess substrate Regulatory mechanisms –Allosteric –Phosphorylation

Glycolysis Convert Glucose to Pyruvate –Yield 2 ATP + 2 NADH per glucose –Consume 2 ATP to form 2x glyceraldehyde phosphate –Produce 2 ATP + 1 NADH per GAP Carefully controlled –12 different enzyme-catalyzed steps –Limited by phosphofructokinase –Limited by substrate availability

Glycolysis/Gluconeogenesis  -D-Glucose-1P  -D-Glucose-6P  -D-Fructose-6P  -D-Fructose-1,6,P2 Glyceraldehyde-3P Glycerate-1,3P2 Glycerate-3P Phosphoenolpyruvate Pyruvate phosphoglucomutase glucose-6-phosphate isomerase 6-phosphofructokinase fructose-bisphosphate aldolase fructose-1,6- bisphosphatase Glycerate-2P GAPDH phosphoglycerate kinase phosphoglycerate mutase enolase pyruvate kinase Hexose import Starch/glycogen breakdown Except for these steps, glycolysis happily runs backward. Backwards glycolysis is gluconeogenesis

Glycolysis: phosphorylation ATP consuming –Glucose phosphorylation by hexokinase –Fructose phosphorylation by phosphofructokinase Triose phosphate isomerase

Glycolysis: oxidation Pyruvate kinase –Transfer Pi to ADP –Driven by oxidative potential of 2’ O Summary –Start C 6 H 12 O 6 –End 2xC 3 H 3 O 3 –Added 0xO –Lost 6xH –Gained 2xNADH, 2xATP NADH ATP pyruvate kinase GAPDH phosphoglycerate kinase

Pyruvate Lactic Acid –Regenerates NAD+ –Redox neutral Ethanol –Regenerates NAD+ –Redox neutral Acetyl-CoA –Pyruvate import to mitocondria –~15 more ATP per pyruvate pyruvate 2-Hydroxyethyl- Thiamine diphosphate S-acetyldihydro- lipoyllysine Acetyl-CoA

Carbohydrate Transport H+, pyruvate cotransporter Halestrap & Price 1999 Major Facilitator Superfamily Monocarboxylate transporter Competition between H+ driven transport to mitochondria and NADH/H+ driven conversion to lactate Cytoplasmic NADH is also used to generate mitochondrial FADH2, coupling transport to ETC saturation “glycerol-3P shuttle”

Gluconeogenesis Regenerate glucose from metabolites –Mostly liver –Many glycolytic enzymes are reversible Special enzymes –Pyruvate carboxylase Generate 4-C oxaloacetate from 3-C pyruvate –Phosphoenyl pyruvate carboxykinase Swap carboxyl group for phosphate Generates 3-C phosphoenolpyruvate from OA –Fructose-1,6-bisphosphatase Generates fructose-6-phosphate Mitochondrial

Glycogen Glucose polysaccharide –Intracellular carbohydrate store –Easily converted to glucose Glycogenolysis –Phosphorylase generates glucose-1-P from glycogen Glycogenesis –Glycogen synthase adds UDP-glucose-1-P to glycogen

Substrate control of CHO metabolism Kinetic flux balance Competition for energy-related molecules –Oxaloacetate: endpoint of TCA –Pyruvate Allosteric regulation by energy-related molecules –ATP/AMP: PFK/PFP –F-1,6-BP: pyruvate kinase –Fatty acids

Substrate competition Oxaloacetate –Oxa + AcCoA  citrate –Oxa + GTP  GDP + PEP Acetyl-CoA –Oxa + AcCoA  citrate –AcCoA + HCO3  MalonylCoA  fatty acids –Amino acid synthesis Oxaloacetate Citrate = Phosphoenylpyruvate

Adenine nucleotides balance glucose breakdown PFK activity depends on ATP/AMP –Competitive binding to regulatory domain PFP activity depends on AMP/citrate ATP AMP PFKPFP Glycolysis PFKGlycolysisATP AMP PFPGlycolysisAMP

Pyruvate kinase Substrate cooperativity Fructose 1,6-bisphosphate Mansour & Ahlfors, cAMP

Hormonal control of CHO metabolism Liver/periphery (liver/muscle) –Glucagon – glucose release –Insulin – glucose uptake System wide response –Distribution of receptors –Tissue specialization Effector systems –Glucose uptake –PFK/PFP balance

Systemic Regulation of Blood Sugar Pancreas –  -cells:Glucose  ATP--|K ATP --| depolarization  Ca  insulin+GABA release –  -cells:GABA  Cl- --|glucagon Peripheral tissues –Insulin  IR  PI3K  GLUT4 translocation  glucose uptake – PI3K  PKB--|GSK--|GS Liver –Glucagon  GR  Gs  AC  PKA--|GS Glucagon Glycogenolysis (Liver) Blood glucose Insulin Glucose uptake, glycogenesis (muscle)

Glucagon Endocrine factor, Gs coupled receptor PLC, AC enhance glycogenolysis –Rapid secretion of glucose from liver Jiang, G. et al. Am J Physiol Endocrinol Metab 284: E671-E ; doi: /ajpendo PLC AC Tiedgen & Seitz, 1980 Insulin/Glucagon ratio Hepatic cAMP

Glucagon:Insulin Glucagon –Liver only –GPCR PLC Adenylate cyclase –Activates GP –Inhibits GS –Stimulates gluconeogenesis Insulin –Most tissues –RTK PI-3K PP1 –Activates GS –Inhibits GP –GLUT-4 translocation Glucose storage (muscle) Glucose distribution (liver)

Phospho-regulation of glycogen The straight activity version PKA +GP via phosphorylase kinase -GS -PP1 via G-subunit PKB +GS via GSK +PP1 via G-subunit PP1 +GS -GP PKAPKB PK PP1-G GS PP1-G GS GP PP1 GSK3 Glycogen Synthesis GP Activates Inhibits

Phospho-regulation of glycogen The phosphorylation story PKA +GP via phosphorylase kinase -GS -PP1 via G-subunit PKB +GS via GSK +PP1 via G-subunit PP1 +GS -GP PKAPKB PK PP1-G GS PP1-G GS GP PP1 GSK3 Glycogen Synthesis GP Phos/Increase Dephos/Decr ActiveInactive