Proteins can undergo chemical modifications such as glycation, which occurs when glucose and other free aldoses spontaneously react with N-terminal and eta-amino groups of proteins to form Schiff bases, which slowly rearrange to ketosamines or, if the sugar was glucose, fructosamines. Fructosamines can further react slowly and become advanced glycation end products, which are thought to play a role in the pathophysiology of several disorders, especially diabetic complications. Ketosamine-3-kinase (FN3K) and ketosamine-3-kinase-related protein (FN3KRP) can phosphorylate protein-bound or free ketosamines on the third carbon of the sugar moiety and the resultant, unstable ketosamine 3-phosphates decompose under physiological conditions (a process called deglycation). Both enzymes can 3-phosphorylate psicosamines (PsiAm) and ribulosamines (RibAm) (Collard et al. 2003, 2004), but only FN3K can 3-phosphorylate fructosamines (FruAm) as well.