Download Mitochondrial Inputs - School of Applied Physiology

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
Starch/glycogen breakdown
Glyceraldehyde-3P
Hexose import
GAPDH
a-D-Glucose-1P
Glycerate-1,3P2
phosphoglucomutase
phosphoglycerate kinase
a-D-Glucose-6P
Glycerate-3P
glucose-6-phosphate isomerase
phosphoglycerate mutase
b-D-Fructose-6P
fructose-1,6bisphosphatase
Glycerate-2P
6-phosphofructokinase
b-D-Fructose-1,6,P2
fructose-bisphosphate aldolase
Except for these steps, glycolysis
happily runs backward. Backwards
glycolysis is gluconeogenesis
enolase
Phosphoenolpyruvate
pyruvate kinase
Pyruvate
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
GAPDH
NADH
ATP
– Start C6H12O6
– End 2xC3H3O3
– Added 0xO
– Lost 6xH
– Gained 2xNADH, 2xATP
phosphoglycerate kinase
pyruvate 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-HydroxyethylThiamine diphosphate
S-acetyldihydrolipoyllysine
Acetyl-CoA
Carbohydrate Transport
• H+, pyruvate cotransporter
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”
Halestrap & Price 1999
Gluconeogenesis
• Regenerate glucose from metabolites
– Mostly liver
– Many glycolytic enzymes are reversible
• Special enzymes
• 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
– Pyruvate carboxylase
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
Oxaloacetate
Citrate
=
Phosphoenylpyruvate
– Oxa + AcCoA  citrate
– AcCoA + HCO3  MalonylCoA fatty acids
– Amino acid synthesis
Adenine nucleotides balance glucose breakdown
• PFK activity depends on ATP/AMP
– Competitive binding to regulatory domain
• PFP activity depends on AMP/citrate
ATP
PFK
PFP
AMP
AMP
Glycolysis
PFK
Glycolysis
ATP
PFP
Glycolysis
AMP
Pyruvate kinase
• Substrate cooperativity
• Fructose 1,6-bisphosphate
+cAMP
Mansour & Ahlfors, 1968
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
– b-cells:GlucoseATP--|KATP--|
depolarizationCainsulin+GABA release
– a-cells:GABACl- --|glucagon
• Peripheral tissues
– Insulin  IRPI3KGLUT4 translocation glucose uptake
–
PI3KPKB--|GSK--|GS
• Liver
– GlucagonGRGsACPKA--|GS
Glucose uptake,
glycogenesis
(muscle)
Insulin
Blood
glucose
Glucagon
Glycogenolysis
(Liver)
Glucagon
• Endocrine factor, Gs coupled receptor
• PLC, AC enhance glycogenolysis
– Rapid secretion of glucose from liver
AC
Hepatic cAMP
PLC
Jiang, G. et al. Am J Physiol Endocrinol Metab 284: E671-E678 2003;
doi:10.1152/ajpendo.00492.2002
Insulin/Glucagon ratio
Tiedgen & Seitz, 1980
Glucagon:Insulin
• Glucagon
– Liver only
– GPCR
• PLC
• Adenylate cyclase
– Activates GP
– Inhibits GS
– Stimulates
gluconeogenesis
Glucose distribution
(liver)
• Insulin
– Most tissues
– RTK
• PI-3K
• PP1
– Activates GS
– Inhibits GP
– GLUT-4 translocation
Glucose storage
(muscle)
Phospho-regulation of glycogen
The straight activity version
• PKA
• PKB
+GP via phosphorylase
kinase
-GS
-PP1 via G-subunit
+GS via GSK
+PP1 via G-subunit
•PP1
+GS
-GP
PK
PKA
GP
PP1-G
GS
PP1
Activates
Inhibits
GP
Glycogen
Synthesis
PP1
PP1-G
GS
GSK3
PKB
Phospho-regulation of glycogen
The phosphorylation story
• PKA
• PKB
+GP via phosphorylase
kinase
-GS
-PP1 via G-subunit
+GS via GSK
+PP1 via G-subunit
•PP1
+GS
-GP
Phos/Increase
Dephos/Decr
Active
PK
PKA
GP
PP1-G
GS
PP1
Inactive
GP
Glycogen
Synthesis
PP1
PP1-G
GS
GSK3
PKB