Inositol 1,3,4,5,6-pentakisphosphate kinase (IP(5) 2-K) is an enzyme involved in inositol metabolism that synthesizes IP(6) (inositol 1,2,3,4,5,6-hexakisphosphate) from inositol 1,3,4,5,6-pentakisphosphate (IP(5)) and ATP. IP(6) is the major phosphorus reserve in plants, while in mammals it is involved in multiple cellular events such as DNA editing and chromatin remodelling. In addition, IP(6) is the precursor of other highly phosphorylated inositols which also play highly relevant roles. IP(5) 2-K is the only enzyme that phosphorylates the 2-OH axial position of the inositide and understanding its molecular mechanism of substrate specificity is of great interest in cell biology. IP(5) 2-K from Arabidopsis thaliana has been expressed in Escherichia coli as two different fusion proteins and purified. Both protein preparations yielded crystals of different quality, always in the presence of IP(6). The best crystals obtained for X-ray crystallographic analysis belonged to space group P2(1)2(1)2(1), with unit-cell parameters a = 58.124, b = 113.591, c = 142.478 A. Several diffraction data sets were collected for the native enzyme and two heavy-atom derivatives using a synchrotron source.