INHIBITION OF PORCINE BRAIN INOSITOL 1,3,4-TRISPHOSPHATE KINASE BY INOSITOL POLYPHOSPHATES, OTHER POLYOL PHOSPHATES, POLYANIONS AND POLYCATIONS

We have partially purified an enzyme activity that phosphorylates inositol 1,3,4-trisphosphate from porcine brain, rat liver and bovine testis by FPLC chromatography on Q-Sepharose anion-exchange resin and Heparin-agarose. The products of this reaction were inositol 1,3,4,6-tetrakisphosphate and inositol 1,3,4,5-tetrakisphosphate. The same enzyme appears to be responsible for both 6-kinase and 5-kinase activities against inositol 1,3,4-trisphosphate (the 6-kinase: 5-kinase activity ratio is approximately 4 to 1), has a pH optimum of similar to 6.8 and requires Mg2+ for activity. The K-m values of the enzyme for inositol 1,3,4-trisphosphate and ATP were similar to 0.5 mu M and similar to 100 mu M, respectively. Inositol 3,4,5,6-tetrakisphosphate, inositol 1,3,4,6-tetrakisphosphate and inositol 1,3,4,5-tetrakisphosphate are all competitive inhibitors with K-i values of 0.4 mu M, 3 mu M and 5 mu M, respectively, well within their likely intracellular concentration ranges: they inhibited 6-kinase and 5-kinase activities equally. 2,3-Bisphosphoglycerate and spermine were also competitive inhibitors, with K-i values of 0.8 mM and 12 mM, respectively. Dextran sulphate was a non-competitive inhibitor with a K-i of similar to 15 mu M, and poly-L-lysine (IC50 similar to 200 mu M), polyvinylsulphate (IC50 similar to 250 mu M) and heparin(IC50 similar to 2 mg/ml) also inhibited. Inhibition by these compounds suggests that inositol 3,4,5,6-tetrakisphosphate (and to a lesser extent inositol 1,3,4,5-tetrakisphosphate and other naturally occurring intracellular ions) may restrict the synthesis of inositol 1,3,4,6-tetrakisphosphate and hence regulate the rate of inositol penta- and hexakisphosphate synthesis from receptor-generated inositol phosphates.