The in vivo formation of fructosamines following non-enzymatic reaction of proteins with glucose (i.e. glycation) was first described almost 30 years ago. Until recently, the only known fate of fructosamines in mammalian cells was their spontaneous conversion into advanced glycation end products. The identification in human erythrocytes of a new enzyme, fructosamine 3-kinase, disclosed the existence of a so-far unsuspected intracellular metabolism of these compounds. Fructosamine 3-kinase phosphorylates with high affinity both low-molecular-mass and protein-bound fructosamines on the third carbon of their deoxyfructose moiety, leading to the formation of fructosamine 3-phosphates. The latter are unstable and spontaneously decompose into inorganic phosphate and 3-deoxyglucosone, with concomitant regeneration of the unglycated amine. The presence of proteins related to fructosamine 3-kinase in many prokaryotic and eukaryotic genomes suggests that this ‘deglycation’ process is not restricted to mammals.

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