SPECIFICITY OF THE PURIFIED INOSITOL (1,3,4,5)-TETRAKISPHOSPHATE-BINDING PROTEIN FROM PORCINE PLATELETS

The specificity of the inositol 1,3,4,5-tetrakisphosphate binding prot ein purified from porcine platelets [Cullen et al. (1995) Biochem. J. 305, 139-143] was examined using all the isomers of myo-inositol tetra kisphosphate. From the relative potencies of these compounds it appear s that phosphorylation of the 1, 3 and 5 positions is essential for hi gh affinity binding, that there is some tolerance of phosphorylation o f the 6-hydroxyl, but none of a phosphate in the 2-position, and that phosphorylation of the 4-hydroxyl has very little influence. The bindi ng of Ins(1,3,4,5)P-4 was not appreciably altered by physiological Mg2 (+) concentrations, and the pH dependence of binding under physiologic al conditions showed a decline from pH 5.5 to pH 9.0.