Ribose 5Phosphate: A Molecule for the AGEs

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Ribose 5-Phosphate A Molecule for the AGEs?

• Roger K. Sandwick
• Department of Chemistry and Biochemistry
• Middlebury College

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Louis-Camille Maillard (1878-1936)

• French researcher in late 1800s/early 1900s
• Reported on sugar/amino acid reactions
  1912-1917

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Maillard Reaction
Heat
Sugar Amine
Melanoidins
(brown polymeric compounds)
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Maillard browning

• 1941 Weast and McKinney darkening of fruits
• 1948 Henry et al. off colors and loss of
  nutritional value in dried milk
• 1951 Patron other sugars, SO2 inhibition

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Colors
Aromas
Maillard Reaction
Flavors
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The Pop Tart
Pop-TartsApple Cinnamon IngredientsApple
filling (corn syrup, dextrose, high fructose corn
syrup, crackermeal, partially hydrogenated
soybean oil, modified wheat starch, dried apples,
malic acid, natural and artificial apple flavor,
sugar, pectin soy lecithin), enriched wheat
flour, partially hydrogenated soybean oil, corn
syrup, high fructose corn syrup, sugar, dextrose,
salt, cinnamon, leavening (baking soda, sodium
acid pyrophosphate, monocalcium phosphate), corn
starch, niacinamide, reduced iron, vitamin A
palmitate, pyridoxine hydrochloride (vitamin B6),
riboflavin (vitamin B2), thiamin hydrochloride
(vitamin B1), and folic acid.
Kellogg Company
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Caramelization

• to convert into a liquid made by cooking sugar
  until it changes color

burns!!
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Maillard Reaction vs.
Caramelization
Caramelization
Maillard Reaction
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Acrylamide in Food
Acrylamide
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Maillard Reaction Acrylamide
Asparagine
Acrylamide
Fructosamine
Glucose
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Acrylamide Levels in Foods

• Acrylamide
  (mg/kg)
• French fries 300 - 700
• Potato chips 600 - 2000
• Boiled Potatoes lt 30
• Pop corn 400
• Coffee (powder) 200
• Breakfast cereals 50 - 250
• Meat lt 30 - 50
• Beer lt 30

Adapted from Acrylamide in Food Swedish
Scientific Expert Committee
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Advanced Glycation End- Products
(AGEs)

• 1967 Samuel Rahbar discovered HbA1C in diabetic
  patients

Samuel Rahbar
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Advanced Glycation End- Products
(AGEs)

• A fast moving Hb band was the result of a
  glycation of the N-terminal valine of the
  b-chain.
• Production of fructosamine, a resulting AGE.
• ADA recommendation - lt 7 HbA1c

Picture from Mosca et al., Clin. Chem. 44, 632 -
638
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Advanced Glycation End- Products
(AGEs)
Pentosidine
Pyrraline
Carboxymethyl- lysine
Imidazolone
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Ribose 5-Phosphate (R5P)

• a phosphorylated aldopentose
• a component of the pentose phosphate pathway
• the starting material for nucleotides, some
  amino acids, and some co-factors

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R5P Shows Enhanced Reactivity
R5P
Glucose
-- 0.1 M Gly 0.05 M sugar at 37 C and pH 8
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R5P Shows Enhanced Reactivity
R5P Glycine Glucose
Glycine
Microwaved 35 seconds
Microwaved 35 seconds
Held at 37 C for 24 h
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The Role of the Phosphate in R5P
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The Role of the Phosphate in R5P
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The Role of the Phosphate in R5P
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The Role of the Phosphate in R5P
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The Role of the Phosphate in R5P
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The Role of the Phosphate in R5P
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Mechanism of Phosphate Catalysis?
Encouragement of the acyclic form
General base catalysis
Stabilization of an oxonium ion
Covalent catalysis
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NMR Study of R5P Loss
 
Gly
DOH
b-peak
a-peak
72 h
Reaction of R5P with glycine at pH 8 and 37 C
24 h
8.7 h
0 h
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R5P and the Maillard Reaction
Speculative Pathway
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R5P Reactivity with Proteins
SDS-PAGE
4 h 6 h 24 h 1 h 2 h His
Reaction of R5P with histones at pH 7.5 and 37 C
66,000
44,000
29,500
14,500
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Some Conclusions

• R5P reacts with amines at a significantly (50
  500 x) faster rate than other common pentose and
  hexose sugars.
• The reaction rate to form UV absorbing compounds
  is related to the pKa of the attacking amine and
  appears to be 1st order in respect to amine and
  1.5 order in respect to R5P.
• R5P has a potential to rapidly cross-link
  proteins, producing both free and protein-bound
  melanoidins.

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Acknowledgements

• Funding
• - AAAS/Merck
• - Vermont Genetics Network
• - Middlebury College

• Researchers
• - Matthew Johanson
• - Elizabeth Breuer
• - Sarah Sandwick
• - Ryan Gamble
• - Admire Muranaire