Protein glycation reactions

The reactions of the early and intermediate stages of protein glycation were studied using bovine serum albumin and hen egg white lysozyme as model proteins, and D-glucose and D-fructose as model reducing sugars. The reactions were studied under low moisture and limiting sugar conditions in the presence and absence of oxygen in a closed system. Several analytical methods, including the fluorescamine assay, total Maillard fluorescence and solubility measurement, size exclusion chromatography, and electrospray ionization mass spectrometry were used to follow the glycation reaction. The effect of glycation on the structure of proteins was also studied by electrospray ionization mass spectrometric peptide mapping. The results showed that under low moisture conditions, the initial rate of glucation was 5 to 6 times higher than the initial rate of fructation, both in the presence and in the absence of oxygen. The presence of oxygen in the reaction system induced selectivity of the glycation of the protein amino groups during the initial stages of the reaction, due to competition between glycation and glycoxidation. The reaction, however, occurred at a higher rate in the presence of oxygen than in its absence, especially during the latter stages of the reaction. The more reactive glycoxidation products, formed during the initial stages of the reaction also participated in the glycation reaction and increased the involvement of arginine residues in the glycation reaction. The glycation reaction also resulted in a heterogeneous mixture of protein glycoforms with varying degrees and extent of glycation. The heterogeneity of the glycated species was further complicated by the involvement of glycoxidation products in the glycation reaction, resulting in a distribution of different classes of glycoconjugates. Limited glycation improved protein solubility and increased solvent accessibility into the interior of the protein, thereby, increasing protein digestibility. Electrosp