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 - Monosaccharides - AldosesAldoses
# Isomers = 2n wheren = # of chiral carbons
Epimers – differ in configuration at only one chiral carbon
Enantiomer
Distant chiral CFrom most oxidized
Not all made in nature
Monosaccharides - Monosaccharides - KetosesKetoses
# Isomers = 2n wheren = # of chiral carbons
Cyclization - aldohexoseCyclization - 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 HaworthBulky substituent on highest numbered
carbon points up
rapid equilibrium Anomers
Hemiacetal
Cyclization - aldopentoseCyclization - aldopentose
Haworthprojection
Anomers
Equilibrium
Anomeric C
Glycolysis: Steps 2 and 3Glycolysis: Steps 2 and 3
Stereospecific: uses -Glc; produces 100% -D-fructose-6-phosphate
Opens the chainduring the rxn
PFK-1
utilizes 100% -anomer
36% -fructose 64% -fructose
CH2OH
OH
Glycoside Bonds – DisaccharidesGlycoside Bonds – Disaccharides
Hemiacetals -a reactive carbonyl that can be oxidized.
reducingnon-reducing
non-reducing sugar
No open chain equil
anomer: refers to free C1 OH
Glycoside Bonds – Glycoside Bonds – DisaccharidesDisaccharides
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
300- 15,000 Glc residues
180 deg rotation
termites
Rigid extended conformationH-bondingForms bundles or fibrils
Cellulose -(1-4) linkage
Polysaccharides – Glucose Storage
Amylose
Amylopectinand
Glycogen
• Plant starch – mixture of amylose and amylopectin
• Animals glycogen
No template (ie no gene)
Homoglycans- one type of monosaccharide
100-1000 glucose residues (maltose units)
Amylopectin:branch every 25 residues
Glycogen:branch every 8-12 residues
10% mass of liver
Polysaccharides -Polysaccharides -Starch DegradationStarch 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 MetabolismGlycogen 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-existingGlycogenin primer
Key regulationby 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 ofsyn and degradation
Sequential removal of GlcFrom non-reducing end
Stops 4 Glc from branch pt
Energy yield from glycogenHigher 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-P glucogen
glucogen
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
XTwo inherited metabolic errors
Hypolactasia (lactose intolerance)
Galactosemia
Lactose Intolerance
Single gene defect
X
Normal decrease in enzyme by 6 yrs old10% 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 gasLactose passes intact into colon
Mutation in chromosome 2
Avoid dietary lactoseTake 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 allowingdiffusion of water into eye
Glucose metabolism
Glc 6-P
Glc
Fruc 6-P
Fruc 1,6-P
Glc Glc 1-P glucogen
glucogen
Glycolysis and CancerGlycolysis and Cancer
Net Reaction:Glucose + 2 ADP + 2 NAD+ + 2 Pi 2 Pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O
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 O2
Cells switch to reliance to glycolysis
Glycolysis and CancerGlycolysis 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
ADP
ATPADP
ATP
ADP
ATPADP
ATP
NADH + H+
NAD+ + Pi
NADH + H+
NAD+ + Pi
H2O H2O
Phosphorylation
Phosphorylation
Substrate Level Phosphorylation
Substrate Level Phosphorylation
Oxidation and Phosphorylation
Isomerization
Cleavage
Isomerization
Rearrangement
Dehydration
Know key reg steps!
Enzymatic Regulation of GlycolysisEnzymatic Regulation of Glycolysis
CAC intermediates, slow down, there is already adequatesupply 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 IsozymesGlycolysis: Hexokinase Isozymes
Can’t leave the cell with negative charge
I-III IV
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-P glucogen
Insulin Dependent UptakeMuscleAdipose
Hormones InvolvedHigh blood [Glc], insulin releasedLow blood [Glc], glucagon released
in Liver
Major function of liver: maintain constant level of Glc in bloodRelease 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-phosphataseGlucose 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-1Regulation 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 KinaseRegulation 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 MetabolismRegulation of Glycogen MetabolismHormonal Regulation:
Via cAMP
Via PIP3
Fed statefasting
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
glycogen PPP
Glc also syn from pyruvate (lactate and amino acids) Liver/kidney
Glc needed in brain/muscle
Gluconeogenesis Gluconeogenesis
Liver
- 3 places differ- control points in glycolysis - 4 new enzymes
ATP energy, NADH reducing equivalents consumed
Gluconeogenesis: Regulation: Regulation
Low [Glc]: glucagon increases protein kinase A (activates Fru-2,6-bisP phosphatase) lowering [Fru-2,6-bisP].
Activate Glc synand
Loss of glycolysis stim
Modulate one enzyme and affect 2 opposing pathways
Sensitive regulatory point
Regulation of Glycogen MetabolismRegulation of Glycogen MetabolismHormonal Regulation:
Via cAMP
Via PIP3
Fed statefasting
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]Simultaneouseffect
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 diseaseUnderstand 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-P glucogen
glucogen
X
X XX
IIV
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 muscleVII
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 normalEffective utilization of muscle glycogen not essential to life
Can’t provide fuel for glycolysis to keep upDemand for ATP
Muscle cramps correlate with inc ADP
Vasodialation-muscle now has access to Glcand fatty acids in blood
NMR on forearm muscle