AN APPLE A DAY KEEPS THE DOCTOR IN PAY

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AN APPLE A DAY KEEPS THE DOCTOR IN PAY
http//www.toothpastefordinner.com/
BCHM2972 Lecture 10 2006
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Presentation and history

• A 10-year old girl, Jane, has a long history of
  problems after eating fruit or any foods
  containing sugar.
• The symptoms include vomiting, stomach cramps,
  trembling, sweating, dizziness, convulsions. 
• 'sickly' since weaned from breast milk to infant
  formula and solids. 
• OK foods? ? trial and error.
• glucose OK but she does not enjoy the taste.
• cow's milk OK
• ?physical development
• Difficult to maintain sugar free diet.
• teeth show no caries!

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• Jane has presented at hospital tonight with
  violent convulsions which were preceded by
  stomach cramps and sweating.
• After soft drink and lollies at a friend's
  slumber party (peer pressure!)
• Refer to the handout of Test results

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What is the likely cause of the sweats,
convulsions, etc?

• A Hypoglycemia
• B Hyperglycemia
• C Hypoinsulinemia
• D Hyperfructosemia

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Which sugars is Jane reacting to?

1. glucose
2. sucrose
3. galactose
4. fructose
5. lactose

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Which sugars is Jane reacting to?
?

1. glucose
2. sucrose
3. galactose
4. fructose
5. lactose

• We know
• foods with glucose OK
• cows milk OK
• FRUIT a problem
• lollies and soft drinks too

?
?
monosaccharides
sucrose
fructose glucose
invertase
in small intestine
absorbed to blood
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soa problem with fructoseinborn error of
metabolism?

• no fructose in breast milk!
• ?Aldolase B not expressed in infants

• long history
• always sickly since weaning
• Why not since birth?

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fructose tolerance testinfuse 200mg/kg fructose
intravenously
which do you expect to be abnormal?

• measure blood levels of
• fructose
• glucose
• phosphorus
• magnesium
• uric acid

confirmed blood test levels are in response to
fructose
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What the?

• Jane has a problem eating fructose, but fructose
  clearance is normal !!
• Why is glucose ? ? (? symptoms) ?
• and why ? P and ? Mg?
• and uric acid and bilirubin??
• dont these mean liver damage?

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• It appears fructose is very efficiently taken up
  and trapped in tissues
• it's the metabolism of the fructose in the
  tissues that's the problem

So..lets review sugar metabolism
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nucleophile (donates e-)
1st step in glycolysis
Breakage of the Phosphoanhydride Bond in ATP
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Glucose
ATP
P
PHOSPHORYLATION
hexokinase
isomerase
ISOMERISATION
Fructose 6 P
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glycolysis
ATP
phospho fructo kinase
PHOSPHORYLATION
Aldolase A
CLEAVAGE
30 ATP per glucose
P
P
GA 3 P
DHAP
CITRIC ACID CYCLE
electron transport and OxPhos
Pyr deHydr
ATP
pyruvate
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Glucose
Fructose
ATP
P
hexokinase
ATP
hexokinase
isomerase
? affinity for fructose
Fructose 6 P
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glycolysis
phospho fructo kinase
in muscle, fat cells
ATP
Aldolase A
P
P
GA 3 P
DHAP
CITRIC ACID CYCLE
electron transport and OxPhos
ATP
pyruvate
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Glucose
Fructose
ATP
ATP
hexokinase
fructokinase
in liverhexokinase has ?affinity for glucose but
?affinity for fructose. lots of glucose in liver
so instead of hexokinase, fructokinase adds P to
trap fructose in cells
Fructose 1 P
Fructose 6 P
1
6
ATP
glycolysis
Aldolase B
ATP
P
P
Glyceraldehyde (GA)
P
GA 3 P
DHAP
DHAP
CITRIC ACID CYCLE
electron transport and OxPhos
ATP
pyruvate
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What is the result of the first step in fructose
metabolism?

1. phosphorylation of fructose
2. ATP used up to phlate fructose
3. cellular energy is reduced
4. phosphate trapped in fructose 1 P
5. all of the above

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What is the result of a mutation in fructokinase?

1. cant phlate fructose ? fructose- 1P
2. reduced clearance of fructose from blood
3. blood fructose remains high
4. ATP not used to plate fructose
5. all of the above

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Can Janes liver trap fructose in the tissue
(clearing it from blood)?

1. Yes
2. No

Does Jane have a mutation in fructokinase?

1. Yes
2. No

Her blood fructose does not rise rapidly after
the fructose load because fructokinase is very
good a mopping up and trapping fructose in the
liver. And/or hexokinase in other tissues is very
good at mopping up fructose into F6P
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Which enzyme catalyses the second step of
fructose catabolism?

• hexokinase
• fructokinase
• phosphofructokinase
• aldolase A
• aldolase B

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What is the result of a mutation in aldolase B?

1. fructose -1P builds up
2. phlation of F-1P uses up ATP
3. cellular energy is reduced
4. phosphate trapped in fructose- 1 P
5. all of the above

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?Fructose
Glucose
?ATP
fructokinase
ATP
ATP
1
?Fructose 1 P
glycolysis
Aldolase B
pyruvate
30 ATP
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Why the ? Pblood?
How do we explain Janes results by a mutation in
aldolase B?

1. P trapped in fructose 1-P
2. P trapped in fructose 6-P
3. P trapped in fructose 1, 6 -biP
4. P trapped in glyceraldehyde 3P
5. all of the above

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Why the ? Pblood?
How do we explain Janes results by a mutation in
aldolase B?

1. P trapped in fructose 1-P
2. P trapped in fructose 6-P
3. P trapped in fructose 1, 6 -biP
4. P trapped in glyceraldehyde 3P
5. all of the above

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What are the consequences of ? Pblood?

• ADP P ? ATP
• ?low cellular energy (ATP)
• ?cell damage /death
• ? release of liver enzymes and bilirubin

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Why the high Mg?

• ATP in complex with Mg2
• ?ATP ? Mg2 released to blood

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ATP, Mg2, and ve residues at an enzyme active
site
Since all the negative charges in ATP are
neutralized, ATP is readily approached by
nucleophiles
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substrate level phosphorylation to compensate for
?ATP
Glucose
ATP
P
hexokinase
ATP
ADP
Fructose
isomerase
ADP
AMP
Fructose 6 P
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glycolysis
phospho fructo kinase
ATP
? PFK ? ? rate gylcolysis (important regulatory
point)
Aldolase A
P
P
GA 3 P
DHAP
CITRIC ACID CYCLE
electron transport and OxPhos
ATP
pyruvate
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normally
NAD
PDH
PFK
AcCoA
glucose
pyruvate
glycolysis
NADH
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?NAD
?AMP
glycolysis

PFK
PDH
AcCoA
pyruvate
glucose
NADH
In Janes liver, pyruvate is produced too fast to
enter mitochondria for TCA (PDH is like the
plughole) ?NAD not regenerated
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cell must regenerate NAD to keep glycolysis
running
NAD
glycolysis
lactate
pyruvate
glucose
ATP
NADH

• desperate attempt to make ATP by glycolysis (2
  per glucose)

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What processes normally lead to increased blood
lactate?

• A Decreased liver gluconeogenesis
• B Increased liver glycolysis (This happens in
  Jane via stimulation of PFK by AMP)
• C Increased muscle glycolysis
• D Decreased PDH activity (would ? entry of
  substrates to Citric Acid Cycle)
• E All of the above
• all increase pyr?lactate to regenerate NAD

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Fructose
glycogen phosphorylase
glycogenolysis
ATP
fructokinase
Fructose 1 P
P
Glucose
Aldolase B
fructose 1,6 bisphosphatase
gluconeogenesis
Why is glucose sooooo low? in addition to ??
glycolysis.
Fructose 1,6 BP
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What is ? uric acid blood indicative of?

• A ? cellular 'energy charge'
• B ? rate of deamination of adenosine
• C ? in ATP
• D ? in AMP
• E All of the above
• not to be confused with urea! (product of amino
  acid catabolism)

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uric acid is a product of purine base
degradation
deamination
AMP
inosine MP
uric acid
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What problems can fructose cause for normal
people?

• does NOT stimulate insulin or leptin
• regulators of energy intake and body adiposity
• bypasses phosphofructokinase
• determines the rate of glycolysis (?pyruvate)
• So.. ?? fructose ? ?? acetyl CoA
• ??Lipogenesis
• ? ?liver TG
• ??insulin sensitivity
• ?? VLDL

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Hepatic fructose metabolism A highly lipogenic
pathway.
http//www.nutritionandmetabolism.com/content/figu
res/1743-7075-2-5-2-l.jpg
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In Summary

• You should make a summary diagram yourselves!
• Show main control points, interconnections, and
  show how the non-functioning enzyme?
• lab results