Kinase Family FruK

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Kinase Classification: Group PKL: Family FN3K

Fructosamine 3' Kinase phosphorylates glycated amino acids in proteins as a first step in deglycation.


FN3K is seen in most eukaryotes, but with substantial losses, including most insects, yeasts, amoebozoa and most excavates. It is also found in many bacteria.

Vertebrates have two family members, one of which (FN3K) is a fructosamine-3-kinase and the other is a ketosamine-3-kinase (FN3KRP) [1, 2], phosphorylating amino acids that have reacted with ketoses (monosaccharides with ketone groups, such as fructose, ribulose and dihydroxyacetone). The two genes are chromosomal neighbors in birds and mammals.


Primary amines of proteins can react with sugars such as glucose and accumulate these glycan adducts as they age. FN3K phosphorylates these sugars, leading to non-enzymatic removal of the sugar phosphate, restoring the protein to its native state.


  1. Szwergold BS, Bunker RD, and Loomes KM. The physiological substrates of fructosamine-3-kinase-related-protein (FN3KRP) are intermediates of nonenzymatic reactions between biological amines and ketose sugars (fructation products). Med Hypotheses. 2011 Nov;77(5):739-44. DOI:10.1016/j.mehy.2011.07.027 | PubMed ID:21924559 | HubMed [Szwergold]
  2. Collard F, Delpierre G, Stroobant V, Matthijs G, and Van Schaftingen E. A mammalian protein homologous to fructosamine-3-kinase is a ketosamine-3-kinase acting on psicosamines and ribulosamines but not on fructosamines. Diabetes. 2003 Dec;52(12):2888-95. DOI:10.2337/diabetes.52.12.2888 | PubMed ID:14633848 | HubMed [Collard]
All Medline abstracts: PubMed | HubMed