Isolation of 1-monomethylphosphoinositol 4,5-bisphosphate [a product of methanolysis of inositol 1,2-(cyclic)-4,5-trisphosphate] from Swiss mouse 3T3 cells.

We have noted two previously undescribed inositol polyphosphates in neutral methanol extracts from Swiss mouse 3T3 cells that were grown in [3H]inositol and stimulated with platelet-derived growth factor. They have been identified as 1-monomethylphosphoinositol 4,5-bisphosphate and 1-monomethylphosphoinositol 4-phosphate by comparison to a synthesized standard using HPLC chromatography, paper electrophoresis, and enzymatic dephosphorylation with inositol polyphosphate 5-phosphomonoesterase and intestinal alkaline phosphatase [orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1]. We propose that these compounds are formed by methanolysis of inositol 1,2-(cyclic)-4,5-trisphosphate and inositol 1,2-(cyclic)-4-bisphosphate present in the cells. Inositol cyclic phosphates did not react with neutral methanol in the absence of the cells, which are required for the methanolysis reaction. These findings suggest a role for inositol cyclic phosphates as reactive compounds that are added to as yet unidentified cellular acceptors.