Human diseases of carbohydrate metabolism

1
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
2
Monosaccharides - Aldoses
Isomers 2n where n of chiral carbons
Enantiomer
Distant chiral C From most oxidized
Epimers differ in configuration at only one
chiral carbon
Not all made in nature
3
Monosaccharides - Ketoses
Isomers 2n where n of chiral carbons
4
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
Anomers
rapid equilibrium
5
Cyclization - aldopentose
Equilibrium
Anomeric C
Hemiacetal
Haworth projection
Anomers
6
Glycolysis Steps 2 and 3
Opens the chain during the rxn
PFK-1
CH2OH
OH

utilizes 100 ?-anomer
Stereospecific uses ?-Glc produces 100
?-D-fructose-6-phosphate
36 ?-fructose 64 ?-fructose
7
Glycoside Bonds Disaccharides
No open chain equil
Hemiacetals -a reactive carbonyl that can be
oxidized.
reducing
non-reducing
b anomer refers to free C1 OH
non-reducing sugar
8
Glycoside Bonds Disaccharides
epimer
Most abundant disacc. in nature (plants)
9
Polysaccharides Structure
180 deg rotation
Cellulose b-(1-4) linkage
300- 15,000 Glc residues
Rigid extended conformation H-bonding Forms
bundles or fibrils
Plant cell walls, stems and branches

• Humans dont have
  b-glucosidases
• Microbe that live in ruminants do

termites
10
Polysaccharides Glucose Storage
Homoglycans- one type of monosaccharide

• Plant starch
• mixture of amylose and amylopectin
• Animals glycogen

Amylose
100-1000 glucose residues (maltose units)
Amylopectin and Glycogen
Amylopectin branch every 25 residues
Glycogen branch every 8-12 residues
10 mass of liver
No template (ie no gene)
11
Polysaccharides -Starch Degradation
Know how starch is broken down !

• Humans digest starch via two enzymes
• a -amylase - endoglycosidase of a-(1-4) linkages
  (random)
• debranching enzyme
• (cleaves limit dextrans)
• Higher plants have
• ß- amylase exoglycosidase of a- (1-4) linkages,
  releasing the disaccharide maltose

Single reducing end
multiple non-reducing end
12
Glycogen Metabolism
Synthesis
Different enzymes for syn and degradation
Driven by PPi hydrolysis
Major regulatory step
13
Key regulation by phosphorylation
(hormonally regulated)
Pre-existing Glycogenin primer
Amylo-(1,4 1,6)-transglycolase catalyzes the
branch point. (Alpha 1-6 link)
14
Degradation
Two subunits, two catalytic sites, allosteric
sites. AMP- activator ATP Glc-6-P
inhibitor. Phosphorylation active
(phosphorylase a). Dephosphorylated less active
(phosphorylase b).
Phosphorolysis rxn. Generates phosph-sugar not
free glc
Primary regulation
15
Branching inc speed of syn and degradation
phosphorolytic
Reg by ATP and G-6-P
Sequential removal of Glc From non-reducing
end Stops 4 Glc from branch pt
Primarily by phosphorylation
Consequences of branch
Reducing vs non-reducing ends
solubility
Rate of syn/degradation
Energy yield from glycogen Higher than from glc
16
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
17
a -amylase
lactase
Glc Gal
18
Absorbed from intestine
Major source of energy for nursing animals
In liver
20 of caloric intake of infants
Glc-6-P
19
(No Transcript)
20
Glucose metabolism
lactase
Glc Gal
Glc
glucogen
Glc
Glc 6-P
Glc 1-P
glucogen
Fruc 6-P
Fruc 1,6-P
21
X
Absorbed from intestine
Major source of energy for nursing animals
In liver
20 of caloric intake of infants
X
Two inherited metabolic errors
Glc-6-P
Hypolactasia (lactose intolerance)
Galactosemia
22
Lactose Intolerance
X
Single gene defect
Normal decrease in enzyme by 6 yrs old 10 of
original activity
(Northern Europeans are lactase producing adults)
Mutation in chromosome 2
Lactase deficient people
Lactose passes intact into colon
bacteria in colon ferment to lactic acid, methane
and H gas
Bloated/ gas and diarrhea
Can also hinder absorption of other nutrients
Avoid dietary lactose Take enzyme substitute
23
Galactosemia
X
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
Cataracts (clouding) due to high galactose in
eye. Converted to galactol allowing
diffusion of water into eye
24
Glucose metabolism
Glc
glucogen
Glc
Glc 6-P
Glc 1-P
glucogen
Fruc 6-P
Fruc 1,6-P
25
Glycolysis and Cancer
Defined Glucose is converted anaerobically to
the three carbon acid pyruvate
Net Reaction Glucose 2 ADP 2 NAD 2 Pi ?
2 Pyruvate 2 ATP 2 NADH 2 H 2 H2O
Generates ATP at higher rate than Oxid Phosp
Oxidative phosphorylation allows more energy
extracted from Glc
Otto Warburg-cancer cells utilize glycolysis even
in presence of O2
Aerobic glycolysis Warburg effect
Initial stages of tumor growth vessels grow at
slower rate cells deprived of O2
Cells switch to reliance to glycolysis
Max energy when pyruvate from glycolysis enters
Citric Acid Cycle
26
Glycolysis and Cancer
Continue to rely of Glycolysis even when O2
restored to tumor
Can visualize tumors based on inc sugar uptake
(PET scan)
Treatment?? Blocking lactose dehydrogenase
(block NAD regeneration turn off Glycolysis)
27
Glucose
ATP
Phosphorylation
Hexokinase
ADP
Glucose-6-phosphate
Know key reg steps!
Isomerization
Glucose-6-phosphate isomerase
Fructose-6-phosphate
ATP
Phosphorylation
Phosphofructokinase-1
ADP
Fructose-1,6-bisphosphate
Cleavage
Aldolase
Dihydroxyacetone phosphate
Isomerization
Trios phosphate isomerase
Glyceraldehyde-3-phosphate
Glyceraldehyde-3-phosphate
NAD Pi
Oxidation and Phosphorylation
Glyceraldehyde-3-phosphate dehydrogenase
NAD Pi
NADH H
NADH H
1,3-bisphosphoglycerate
1,3-bisphosphoglycerate
ADP
Substrate Level Phosphorylation
ADP
Phosphoglycerate kinase
ATP
ATP
3-phosphoglycerate
3-phosphoglycerate
Phosphoglycerate mutase
Rearrangement
2-phosphoglycerate
2-phosphoglycerate
Enolase
H2O
Dehydration
H2O
phosphoenolpyruvate
phosphoenolpyruvate
ADP
ADP
Substrate Level Phosphorylation
Pyruvate kinase
ATP
ATP
pyruvate
pyruvate
28
Enzymatic Regulation of Glycolysis
Not moving forward, stop converting ATP
Cellular rxns are converting ATP and ADP, make
more ATP
Youve committed! Bi-phosphated furanoses, keep
pathway moving
CAC intermediates, slow down, there is already
adequate supply of energy
29
Glycolysis Hexokinase Isozymes
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
I-III
IV
Isozymes Different inhibition profiles
Location, Km Control point
Glc
Glc
Glc 6-P
Glc 1-P
glucogen
Cant leave the cell with negative charge
Fruc 6-P
Fruc 1,6-P
30
in Liver
Hormones Involved High blood Glc, insulin
released Low blood Glc, glucagon released
Insulin Dependent Uptake Muscle Adipose
Major function of liver maintain constant level
of Glc in blood Release Glc (from glycogen)
during muscle activity and between meals
31
Glucose 6-phosphatase
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
32
Body does not transfer pyruvate
Lactate- produced in RBC and Muscle
Lactate to pyruvate in liver
Cori cycle
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
33
Regulation of Phosphofructokinase-1
Large oligomeric enzyme bacteria/mammals -
tetramer yeast - octamer
ATP - product of pathway - allosteric
inhibitor
AMP - allosteric activator - relieves
inhibition by ATP
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
34
Regulation of Pyruvate Kinase
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 (feed-forward) activation
Fructose-1,6-bisphosphate -allosterically
activates -produced in step three -links
control steps together
Allosteric inhibition by ATP -product of
pathway and CAC
Low blood Glc
High blood Glc
35
Regulation of Glycogen Metabolism
Hormonal Regulation
Fed state
fasting
Via cAMP
Via PIP3
Insulin secreted by pancreas when Glc high
inc rate of transport into cell and glycogen syn
GLUT4
Glucagon secreted when Glc low
Epi released by adrenal gland in response to
neural signal (flight or flight)
Sudden energy response
36
Gluconeogenesis
Liver
glycogen
PPP
- 3 places differ- control points in glycolysis
- 4 new enzymes
ATP energy, NADH reducing equivalents consumed
Glc also syn from pyruvate (lactate and amino
acids)
Liver/kidney
Glc needed in brain/muscle
37
Gluconeogenesis Regulation
Modulate one enzyme and affect 2 opposing
pathways Sensitive regulatory point
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
38
Regulation of Glycogen Metabolism
Hormonal Regulation
Fed state
fasting
Via cAMP
Via PIP3
Insulin secreted by pancreas when Glc high
inc rate of transport into cell and glycogen syn
GLUT4
Glucagon secreted when Glc low
Epi released by adrenal gland in response to
neural signal (flight or flight)
Sudden energy response
39
Intracellular Regulation of Glycogen Metabolism
by Interconvertible Enzymes
Low glc activate kinase and breakdown
Simultaneous effect
Low Glc
40
High Glc
41
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
Understand how enzyme deficiency leads to
accumulation of glycogen
Glycogen storage disease
Other symptoms
Treatment, if any
42
Glycogen storage disease
Glc
glucogen
X
V
II, III, VI
X
X
Glc
Glc 6-P
Glc 1-P
glucogen
I
IV
Fruc 6-P
All defects lead to glycogen accumulation
X
VII
Fruc 1,6-P
I
Glucose-6-Phosphatase in liver (von Gierks
disease)
Liver enlargement
hypoglycemia (low blood glc) when fasting
Branching enzyme in organs (liver) (Andersent
disease)
IV
Liver dysfunction and early death
Glycogen phosphorylase in muscle (McArdles
disease)
V
Muscle cramps with exercise
Phosphofructokinase in muscle
VII
Inability to exercise
Glycogen accumulation and
43
Glycogen storage disease
Type I
Glucose-6-Phosphatase deficiency in liver (von
Gierks disease)
Glc not released into blood
No response to Epinephrine or Glucagon
hypoglycemia (low blood glc) between meals
infant in convulsions
Large amounts of glycogen in liver (G-6-P
inhibits breakdown)
Liver enlargement
Glc-6-P increases glycolysis inc
lactate/pyruvate in blood
(Lactic acidosis)
Delayed puberty, short stature
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
44
Glycogen storage disease
Type IV
Most severe disease
Branching enzyme deficiency in organs (liver)
(Andersens disease)
Accumulate abnormal glycogen
Reduced solubility of glycogen
Foreign body immune response??
Liver dysfunction
Failure to thrive----- death 2-5 yrs old
45
Glycogen storage disease
Type V
Glycogen phosphorylase deficiency in muscle
(McArdles disease)
No breakdown of glycogen
Exercise indices muscle cramps otherwise
normal
Effective utilization of muscle glycogen not
essential to life
Cant provide fuel for glycolysis to keep
up Demand for ATP
NMR on forearm muscle
Muscle cramps correlate with inc ADP
Vasodialation-muscle now has access to Glc and
fatty acids in blood