Table 2.

Catalytic comparison between WT and H162D mutant of hITPK1

Substrate	Reaction	WT	H162D
Ins(1,4,5)P3	Phosphorylation	0.026 ± 0.001	0.0113 ± 0.003
Ins(1,3,4)P3	Phosphorylation	671 ± 60	3.3 ± 0.4
Ins(3,4,5,6)P4	Phosphorylation	309 ± 57	43 ± 7
Ins(1,3,4,5,6)P5	Dephosphorylation	53 ± 3.3	135 ± 13
Ins(1,3,4,5,6)P5	Dephosphorylation:-fold effect of Ins(1,3,4)P3	2.9 ± 0.4	0.96 ± 0.04
[32P]-Ins(1,3,4,5,6)P5	Phosphate transfer: InsP4 / ATP	31	0.31

Assays were performed as described in the Methods Section. The units for the kinase reactions are 10³ × k (the first-order rate constant) / ng protein. Ins(1,3,4,5,6)P₅ dephosphorylation is measured as nmoles /mg protein / min. The effect of Ins(1,3,4)P₃ upon Ins(1,3,4,5,6)P₅ dephosphorylation is calculated as a ratio: plus Ins(1,3,4)P₃ / minus Ins(1,3,4)P₃. The values for “phosphate transfer” are the ratios of [³²P]-labeled InsP₄ vs ATP, formed after either enzyme dephosphorylated approximately 50% of 5 µM [³²P-1]-Ins(1,3,4,5,6)P₅ substrate, in the presence of 5 µM Ins(1,3,4)P₃ (e.g. see Fig. 1B).