Liver microsomes contain multiple forms of inositol 1,4,5-trisphosphate binding proteins: identification by...

A group of proteins binding to inositol 1,4,5-trisphosphate (IP3) has been identified in rat liver microsomes by a nitrocellulose blot-overlay technique. Proteins were resolved by SDS-PAGE, blotted on nitrocellulose and incubated with [32P]IP3 followed by autoradiography. Approximately eight IP3-binding polypeptides ranging M(r) 23-50 kDA were present exclusively in microsomes; these were absent from plasma membrane and mitochondrial fractions. Binding of [32P]IP3 to these proteins was displaceable to a great extent by 5 microM unlabeled IP3 but not by 10 microM IP1, IP2, IP4, ATP, or GTP gamma S. These results suggest that liver microsomes contain multiple forms of IP3-binding proteins that can be detected by this new method.