Ribose 5 Phosphate A Molecule for the AGEs

Ribose 5 -Phosphate: A Molecule for the AGEs? Roger K. Sandwick Department of Chemistry and Biochemistry Middlebury College

Louis-Camille Maillard (1878 -1936) ■ French researcher in late 1800 s/early 1900 s ■ Reported on sugar/amino acid reactions – 19121917

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

Maillard “browning” n n n 1941 – Weast and Mc. Kinney – darkening of fruits 1948 – Henry et al. – off colors and loss of nutritional value in dried milk 1951 – Patron – other sugars, SO 2 inhibition

Colors Aromas Maillard Reaction 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 B 6), riboflavin (vitamin B 2), thiamin hydrochloride (vitamin B 1), and folic acid. ®Kellogg Company

Caramelization: “to convert into a liquid made by cooking sugar until it changes color” b ! ! s urn

Maillard Reaction vs. Caramelization: Maillard Reaction Caramelization:

Acrylamide in Food Acrylamide

Maillard Reaction & Acrylamide Asparagine Glucose Acrylamide Fructosamine

Acrylamide Levels in Foods French fries Potato chips Boiled Potatoes Pop corn Coffee (powder) Breakfast cereals Meat Beer [Acrylamide] (mg/kg)* 300 - 700 600 - 2000 < 30 ~ 400 ~ 200 50 - 250 < 30 - 50 < 30 * Adapted from “Acrylamide in Food” Swedish Scientific Expert Committee

Advanced Glycation End. Products (AGEs) n 1967 – Samuel Rahbar discovered Hb. A 1 C in diabetic patients Samuel Rahbar

Advanced Glycation End. Products (AGEs) n n n 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 < 7% Hb. A 1 c *Picture from Mosca et al. , Clin. Chem. 44, 632 - 638

Advanced Glycation End. Products (AGEs) Pentosidine Carboxymethyllysine Pyrraline Imidazolone

Ribose 5 -Phosphate (R 5 P) § a phosphorylated aldopentose § a component of the pentose phosphate pathway § the starting material for nucleotides, some amino acids, and some co-factors

R 5 P Shows Enhanced Reactivity R 5 P Glucose -- 0. 1 M Gly + 0. 05 M sugar at 37 C and p. H = 8

R 5 P Shows Enhanced Reactivity R 5 P + Glycine Glucose + Glycine Microwaved – 35 seconds Held at 37 C for 24 h

The Role of the Phosphate in R 5 P

Mechanism of Phosphate Catalysis? Encouragement of the acyclic form Stabilization of an oxonium ion General base catalysis Covalent catalysis

NMR Study of R 5 P Loss Gly DOH a-peak b-peak 72 h Reaction of R 5 P with glycine at p. H = 8 and 37 C 24 h 8. 7 h 0 h

R 5 P and the Maillard Reaction Speculative Pathway

R 5 P Reactivity with Proteins 4 h 6 h 24 h Reaction of R 5 P with histones at p. H =7. 5 and 37 C 1 h 2 h His SDS-PAGE 66, 000 44, 000 29, 500 14, 500

Some Conclusions n n n R 5 P 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 p. Ka of the attacking amine and appears to be 1 st order in respect to [amine] and 1. 5 order in respect to [R 5 P]. R 5 P has a potential to rapidly cross-link proteins, producing both free and proteinbound melanoidins.

Acknowledgements n Researchers - Matthew Johanson - Elizabeth Breuer - Sarah Sandwick - Ryan Gamble - Admire Muranaire n Funding: - AAAS/Merck - Vermont Genetics Network - Middlebury College