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      Mechanism of protein modification by glyoxal and glycolaldehyde, reactive intermediates of the Maillard reaction.

      The Journal of Biological Chemistry
      Acetaldehyde, analogs & derivatives, chemistry, Chromatography, High Pressure Liquid, Chromatography, Thin Layer, Electrophoresis, Polyacrylamide Gel, Gas Chromatography-Mass Spectrometry, Glyoxal, Lysine, chemical synthesis, Maillard Reaction, Oxidation-Reduction, Proteins

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          Abstract

          The role of glyoxal and glycolaldehyde in protein cross-linking and N epsilon-(carboxymethyl)lysine (CML) formation during Maillard reaction under physiological conditions was investigated. Incubation of bovine serum albumin with these reagents lead to rapid formation of C-2-imine cross-links and CML. Initial CML formation rate from glyoxal was not dependent on oxidation, suggesting an intramolecular Cannizzaro reaction. CML formation from glucose/lysine or Amadori product of both was strongly dependent on oxidation. Blocking of Amadori product by boric acid totally suppressed CML formation from Amadori product, but only by 37% in the glucose/lysine system. Trapping of glyoxal with aminoguanidine hardly suppressed CML formation from Amadori product, whereas it blocked 50% of CML production in the glucose/lysine system. While these results would support a significant role for glucose autoxidation in CML formation, the addition of lysine to a glucose/aminoguanidine incubation system catalyzed glyoxal-triazine formation 7-fold, thereby strongly suggesting that glucose autoxidation is not a factor for glyoxal-mediated CML formation. Based on these results, it can be estimated that approximately 50% of the CML forming in a glucose/lysine system originates from oxidation of Amadori product, and 40-50% originates from a pre-Amadori stage largely independent from glucose autoxidation. This step may be related to the so-called Namiki pathway of the Maillard reaction.

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