ITPK1 (Inositol Tetrakisphosphate 1-Kinase), Fig. 1

Schematic of the phosphotransferase activity of ITPK1. The upper reaction depicts the ADP-dependent cleavage of the 1-phosphate from Ins(1,3,4,5,6)P5; the nucleotide is proposed to remain bound to the enzyme (E). The lower reaction depicts ATP-dependent addition of a 6-phosphate to Ins(1,3,4)P3; again, nucleotide is proposed to remain bound to the enzyme. If nucleotide is released, ITPK1 may act as, simply, an Ins(1,3,4)P3 6-kinase or an Ins(1,3,4,5,6)P5 1-phosphatase