Molecular internet ions of synthetic inositol phosphates with inositol 1.4.5-trisphosphate 3-kinase

D-myo-inositol 1.4,5-trisphosphate[Ins( 1,4,5) is a well-known second messen gel which triggers Ca2+ release from the endoplasmic reticuhm, lnositol 1,t,5 trisphosphate 3-kinase(IP3K) catalyzes the ATP-dependent phosphorylation of Ins( 1,4.5)P: generating Ins(1,3,4,5)P4. We investigated the inhibitory effects of all the possible regioisomers from InsPls to InsPss on IP3K activity. IP:IK was very specific for its substrate, Ins( 1,1,5)P:3 while a few inositol phosphates were found to be relatively good inhibitors of IP3K. Ins( 1,4,6)P: wa, the most potent inhibitor of lP3K among the inositol phosphates but did not act as a substrate for the kinase. Since IP3K appears to have a vacant spa((, surrounding the 1,2 position of Ins(1,4,5)P3 with the lining of the space (barged negatively. it binds weakly lns(1,2,4,6)P4 which has a 2-phosphate group. The effect of the phosphate group at the (7-3 position of Ins(1A,5)Pa was very different depending upon its orientation; Ins(1,3,4,5)P4 with the equatorial 3-phosphate group was a weak inhibitor of IP3K, whereas Ins(1,2,4,6 )t',t with the axial 2-phosphate which is equivalent to the 3-phosphate of Ins( 1,3,1,5)1)4. showed strong inhibitory activity on the kinase. These data imply that IPaK has an empty space towards the axial direction on the C-3 position of Ins(l,.l.5)P: . It is suggested that IPaK has the vacant spaces at C-2 and (' 3 positions of Ins( 1.1,-DP: , and the characteristics of these vacant spaces are very different from those of Ins( 1,4,5)P3-receptor.