Responsibility of 3-Deoxyglucosone for the Glucose-Induced Polymerization of Proteins

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Abstract
The present work was conducted to identify the carbonyl compounds responsible for the glucose-induced polymerization of proteins and the impairment of their amino acid residues. Non-nitrogenous intermediate products of the Maillard reaction (IMR) were prepared through the reaction of glucose with butylamine, and the most major product was identified as 3- deoxyglucosone (3DG) by mass spectrometry and 13C NMR. Thus, 3DG was purified from IMR and stored with proteins. 3DG polymerized both lysozyme and acetylated lysozyme, and impaired Arg, Lys and Trp residues of lysozyme, and Arg and Trp residues of acetylated lysozyme, when incubated at 50°C and 75% relative humidity for 3 days. The elution pattern of the impaired Arg residues during an amino acid analysis was exactly the same as that observed in the glucose-induced modification of lysozyme. 3DG induced the same alteration in ovalbumin, bovine serum albumin and insulin, as that in lysozyme. All these results indicate that 3DG was the cross-linker responsible for the glucose-induced polymerization of proteins, and the attacker of their Arg, Lys and Trp residues.