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

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

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, SO 2 inhibition

Maillard Reaction Aromas Colors 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 Acrylamide

Maillard Reaction & Acrylamide Glucose AsparagineAcrylamide Fructosamine

Acrylamide Levels in Foods [Acrylamide] (  g/kg) * French fries Potato chips Boiled Potatoes < 30 Pop corn ~ 400 Coffee (powder) ~ 200 Breakfast cereals Meat< Beer < 30 * Adapted from “ Acrylamide in Food ” Swedish Scientific Expert Committee

Advanced Glycation End- Products (AGEs) 1967 – Samuel Rahbar discovered HbA 1C 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% HbA 1c *Picture from Mosca et al., Clin. Chem. 44,

Advanced Glycation End- Products (AGEs) Pentosidine Carboxymethyl- lysine Pyrraline Imidazolone

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

R5P Shows Enhanced Reactivity M Gly M sugar at 37 C and pH = 8 R5P Glucose

R5P Shows Enhanced Reactivity R5P + Glycine Glucose + Glycine Microwaved – 35 seconds Held at 37 C for 24 h

The Role of the Phosphate in R5P

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

NMR Study of R5P Loss  -peak  -peak DOH Gly 0 h 8.7 h 24 h 72 h Reaction of R5P with glycine at pH = 8 and 37 C

R5P and the Maillard Reaction Speculative Pathway

R5P Reactivity with Proteins 66,000 44,000 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 1 st 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