Solubilization and separation of inositol 1,3,4,5-tetrakisphosphate- and inositol 1,4,5-trisphosphate-binding proteins and metabolizing enzymes in rat brain.

The two inositol phosphate-binding proteins, the Ins(1,4,5)P3 (InsP3) and Ins(1,3,4,5)P4 (InsP4) receptors, and the two particulate InsP3-metabolizing enzymes, InsP3 5-phosphatase and InsP3 3-kinase, were solubilized with detergent from rat cerebellar membranes. These four activities are shown to be distinct molecular species by separation using a variety of protein chromatographic steps. The pharmacology of the partially purified InsP4-binding site indicates that the binding has a high affinity and selectivity for InsP4 over InsP3. These results suggest the existence of a distinct specific InsP4-binding protein which may represent the receptor for this putative second messenger.