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ABSTRACT
Amadoriases are discovered in distant groups of organisms ranging from bacteria to humans. These enzymes catalyze the degradation of Amadori products which are formed in the early stage a non-enzymatic reaction between reducing sugars and primary amines called the Maillard reaction or glycation. The physiological role of amadoriases is debatable and perhaps not constrained to one cellular process only. Among other functions amadoriases are proposed to ensure enzymatic defense against the deleterious consequences of protein glycation. A decade ago an amadoriase enzyme (the FrlB amadoriase) has been discovered in Escherichia coli catalyzing the removal of Amadori products form the ϵ-amino group of free lysine. The E. coli FrlB enzyme has been suggested to catabolize glycated lysine released in the human intestine upon digestion of food proteins. In the present study we demonstrate that the E. coli FrlB amadoriase is capable of catalyzing in the reverse reaction the formation of Amadori products on a number of free amino acids and on polypeptides as well. Based on these results we suggest that in the forward reaction the FrlB enzyme might serve to deglycate E. coli proteins thus helping bacterial cells to withstand the protein glycation burden.