Table 1.

Identification of IP₄ species in cell extracts by enzymatic analysis

Cell extract	Enzymatic treatment, percent conversion				Primary IP4 species
	IPMK	IPK1	5-Ptase	ITPK1
Gaq + IPMK	82	22	11	18	I(1,4,5,6)P4
Gaq + IP3K	92	14	86	0	I(1,3,4,5)P4
Gaq + ITPK1	94	60	32	0	I(1,3,4,6)P4

Cell extracts were prepared from [³H]inositol-labeled 293T cells and were treated enzymatically with IPMK, Ipk1, 5-Ptase, or ITPK1 to identify the major IP₄ species present. Assignments were based on the expected substrates of each enzyme. I(1,4,5,6)P₄ is a substrate for IPMK, I(1,3,4,5)P₄ is a substrate for IPMK and 5-Ptase, I(3,4,5,6)P₄ is a substrate for ITPK1, and I(1,3,4,6)P₄ is a substrate for IMPK and IPK1. Results are expressed as the percentage of the IP₄ peak that was converted by the enzymatic treatment.