Fructosyllysine

Fructosyllysine is a stable Amadori product formed when the carbonyl group of fructose reacts with the ε-amino group of lysine residues in proteins. It is an early stage compound in the Maillard reaction and is commonly treated as a marker of protein glycation, a broader class known as advanced glycation end products (AGEs).

Formation and chemistry: The initial Schiff base forms between fructose and lysine, which rearranges to the Amadori product, yielding fructosyllysine. Fructose, a ketose, can react more rapidly than glucose, leading to higher levels of fructosyllysine in heated or sugar-rich contexts. FL can accumulate in dietary proteins during processing and storage, and similarly can form in vivo under hyperglycemic conditions.

Occurrence and significance: In foods, FL serves as an indicator of the extent of heat-processed glycation and correlates with overall AGE content. In biological samples, FL is used as a biomarker of protein glycation and glycemic exposure; its significance in aging and metabolic disease is an area of research.

Analytical aspects: FL is typically quantified after proteolytic digestion or hydrolysis of proteins, followed by chromatographic methods such as HPLC or LC-MS to detect and quantify the fructosyllysine moiety. Methods may require derivatization or enzymatic digestion to release or stabilize the adduct.