Converts inositol hexakisphosphate (InsP6) to diphosphoinositol pentakisphosphate (InsP7/PP-InsP5). 1D-myo-inositol hexakisphosphate + ATP = 5-diphospho-1D-myo-inositol 1,2,3,4,6-pentakisphosphate + ADP Inhibited by flavonoids, including myricetin, quercetin, luteolin, isorhamnetin, rhamnetin, kaempferol, diosmetin and apigenin. Phospholipid metabolism; phosphatidylinositol metabolism. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay. Belongs to the inositol phosphokinase (IPK) family.