Fructosyl-lysine is the precursor to glucosepane. Fructosyl-lysine is a lysine–arginine protein cross-link that can be an indicator in diabetes detection. Fructosyl-lysine is an amadori glycation product from the reaction of glucose and lysine by the Maillard reaction.

Fructosyl-lysine (100 μM; 1 hour) contains a carbohydrate moiety and appears to be phosphorylated, it can be converted to glucose 6-phosphate in bacterial extracts in?E?.coli extracts. Fructosyl-lysine (25 mM; 25 hours) lets E. coli?growth at a rate of about one-third of that observed with glucose as a carbon source. Fructosyl-lysine (5 mM; 0.5 hours) catalyzes the ATP-dependent conversion of [14C]fructoselysine to anionic products showing the existence of a fructoselysine-kinase activity in E?.coli extracts [2].

In diabetic rats, Fructosyl-lysine and AGE residues are increased markedly in glomeruli, sciatic nerve, retina, and plasma protein [1].