Solubilization, purification, and characterization of an inositol trisphosphate receptor

Inositol 1,4,5-trisphosphate is a second messenger of the phosphoinositide system which can mobilize calcium from intracellular stores. Rat cerebellum is an abundant source of a receptor for inositol 1,4,5-trisphosphate (Worley, P.F., Baraban, J.M., Supattapone, S., Wilson, V.S., and Snyder, S.H. (1987) J. Biol. Chem. 262, 12132-12136). In this study we have solubilized and purified this receptor to apparent homogeneity from rat cerebellum. Crude membrane, detergent-solubilized, and purified receptor preparations display similar selectivity for inositol 1,4,5-trisphosphate over other inositol phosphates. The purified receptor is globular with a Stokes' radius of approximately 10 nm. Electrophoretic analysis reveals one protein band with an M(r) of 260,000. While binding is reversibly inhibited by 300 nM calcium in particulate fractions and detergent-solubilized membranes, the purified protein is not inhibited by calcium concentrations up to 1.5 mM. Inhibition by calcium is reconstituted by addition of detergent-solubilized cerebellar membranes, but not by the cytosolic fraction of cerebellum.