Ribose 5-Phosphate: A Molecule for the AGEs? Roger K. Sandwick Department of Chemistry and Biochemistry Middlebury College
Jan 30, 2016
Ribose 5-Phosphate: A Molecule for the AGEs?
Roger K. SandwickDepartment of Chemistry and Biochemistry
Middlebury College
Louis-Camille Maillard (1878-1936)
■ French researcher in late 1800s/early 1900s
■ Reported on sugar/amino acid reactions – 1912-1917
Maillard Reaction
Sugar + Amine Melanoidins(brown polymeric compounds)
Heat
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
Maillard Reaction
AromasColors
Flavors
The Pop Tart® Pop-Tarts®
Apple Cinnamon
Ingredients:Apple 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
Caramelization:
“to convert into a liquid made by cooking sugar until it changes color” burns!
!
Maillard Reaction vs. Caramelization:
Maillard Reaction Caramelization:
Acrylamide in Food
CH
C
O
NH2
H2C
Acrylamide
Maillard Reaction & Acrylamide
CHO
OHH
HHO
OHH
OHH
CH2OH
H2N
HC
C
O
O-CH2
CO
NH2
+
HC
OHH
HHO
OHH
OHH
CH2OH
NH+
CH
CO
O-
H2C
C
O
NH2
H2C
OHH
HHO
OHH
OHH
CH2OH
NH+
HCH2C
C
O
NH2
H2C
O
HHO
OHH
OHH
CH2OH
NH3+
Glucose
Asparagine
CH
C
O
NH2
H2C
Acrylamide
CO2
Fructosamine
Acrylamide Levels in Foods [Acrylamide] (g/kg)*
French fries 300 - 700Potato chips 600 - 2000Boiled Potatoes < 30Pop corn ~ 400Coffee (powder) ~ 200Breakfast cereals 50 - 250Meat < 30 - 50Beer < 30
* Adapted from “Acrylamide in Food” Swedish Scientific Expert Committee
Advanced Glycation End- Products (AGEs)
1967 – Samuel Rahbar discovered HbA1C in diabetic patients
Samuel Rahbar
Advanced Glycation End- Products (AGEs)
A fast moving Hb band was the result of a glycation of the N-terminal valine of the -chain.
Production of fructosamine, a resulting AGE.
ADA recommendation - < 7% HbA1c
*Picture from Mosca et al., Clin. Chem. 44, 632 - 638
Advanced Glycation End- Products (AGEs)
N+NH
N
HN
(H2C)3
CH(CH2)4
CH
N
CHOHOH2C
CH2CH2CH2CH2
CH
CH
CH2
CH2
CH2
H2C
HNCH2
COOH
NH
NO
H2C
HC
HC
OH
H2C
OH
OH
HN (CH2)3 CH
Pentosidine
Carboxymethyl- lysine
Pyrraline
Imidazolone
Ribose 5-Phosphate (R5P)
H
OH
H
HO OH
H H
O
H
H
OP-O
O-
O a phosphorylated aldopentose
a component of the pentose phosphate pathway
the starting material for nucleotides, some amino acids, and some co-factors
R5P Shows Enhanced Reactivity
-- 0.1 M Gly + 0.05 M sugar at 37 C and pH = 8
Reaction of R5P and Glucose with Glycine
012345678
0 10 20 30 40 50
Time (h)
A28
0
R5P
Glucose
R5P Shows Enhanced Reactivity
R5P + Glycine Glucose + Glycine
Microwaved – 35 seconds Microwaved – 35 seconds
Held at 37 C for 24 h
The Role of the Phosphate in R5P
H
OH
H
HO OH
H H
O
H
H
OP-O
O-
O
The Role of the Phosphate in R5P
H
OH
H
HO OH
H H
O
H
H
OP-O
O-
O
The Role of the Phosphate in R5P
H
OH
H
HO OH
H H
O
H
H
OPO-
O-
O
The Role of the Phosphate in R5P
H
OH
H
HO OH
H H
O
H
H
OP
O-
O-
O
The Role of the Phosphate in R5P
H
OH
H
HO OH
H H
O
H
H
OP
O-
O-
O
The Role of the Phosphate in R5P
H
OH
H
HO OH
H H
O
H
H
OP
O-
O-
O
Mechanism of Phosphate Catalysis?
H
-XO
OH
HH
OHHOH
O P O-
O
O-
H
O
OH
HH
HOH
O P O-
O
O-
H+
+O
OH
HH
HOH
OP
O-
O
O
H
OH
OH
HH
HOH
O PO-
O
-O H+
O
Encouragement of the acyclic
form
Covalent catalysis
General base catalysis
Stabilization of an
oxonium ion
NMR Study of R5P Loss
-peak-peak
DOH Gly
3.54.04.55.05.5 ppm
0 h
8.7 h
24 h
72 h
OH
H
H
HO OH
H H
O
H
H
OP-O
O-
O
H
OH
H
HO OH
H H
O
H
H
OP-O
O-
O
Reaction of R5P with glycine at pH = 8 and 37 C
R5P and the Maillard Reaction
CH
OHH
OHH
OHH
CH2OPO3H-
O
CH
OHH
OHH
OHH
CH2OPO3H-
N+ C COOHH
H
H
CH
OH
OHH
OHH
CH2OPO3H-
N C COOHH
H
H
CH
OH
H
OHH
CH2OPO3H-
N+ C COOHH
H
H
CH
O
HH
OHH
CH2OPO3H-
O
CH2
O
OHH
OHH
CH2OPO3H-
N C COOHH
H
H
CH2
OH
OH
OHH
CH2OPO3H-
N C COOHH
H
H
CH2
OH
O
OHH
CH2OPO3H-
CH3
O
O
OHH
CH2OPO3H-
Gly
Gly
Gly
OH-
OH-
OH-
3--deoxy-2-pentosulose 5-phosphate
1-deoxy-2,3-pentodiulose 5-phosphate
N-(1-deoxy-D-ribos-1-yl)-glycine 5-phosphate
Ribose 5-phosphate
Speculative
Pathway
R5P Reactivity with Proteins
66,00044,000
29,500
14,500
4 h 6 h 24 h 1 h 2 h His
Reaction of R5P with histones at
pH =7.5 and 37 C
SDS-PAGE
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.
Acknowledgements
Funding:
- AAAS/Merck
- Vermont Genetics Network- Middlebury College
Researchers- Matthew Johanson- Elizabeth Breuer- Sarah Sandwick
- Ryan Gamble - Admire
Muranaire