Pathway for inositol 1,3,4-trisphosphate and 1,4-bisphosphate metabolism.
We prepared [3H]inositol-,3-[32P]phosphate-and 4-[32P]phosphate-labeled inositol phosphate substrates to investigate the metabolism of inositol 1,3,4-trisphosphate and inositol 1,4-bisphosphate. In crude extracts of calf brain, inositol 1,3,4-trisphosphate is first converted to inositol 3,4-bisphosphate, then the inositol 3,4-bisphosphate intermediate is further converted to inositol 3-phosphate. Similarly, inositol 1,4-bisphosphate is converted to inositol 4-phosphate, and no inositol 1-phosphate is formed. We partially purified an enzyme that we tentatively name inositol polyphosphate 1-phosphatase. This cytosolic enzyme converts inositol 1,3,4-trisphosphate to inositol 3,4-bisphosphate and also converts inositol 1,4-bisphosphate to inositol 4-phosphate. The enzyme does not utilize inositol 1,3,4,5-tetrakisphosphate, inositol 1,4,5-trisphosphate, or inositol 1-phosphate as substrates. Thus we propose a new scheme for inositol phosphate metabolism. According to this pathway inositol 1,4,5-trisphosphate and inositol 1,4-bisphosphate are degraded to inositol 4-phosphate. Inositol 1-phosphate, which is the major inositol monophosphate formed in stimulated brain, is derived either from phospholipase C cleavage of phosphatidylinositol or from the degradation of inositol cyclic phosphates.
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002417:Cattle; D003600:Cytosol / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000378:metabolism*; D008954:Models, Biological; D010744:Phosphoric Monoester Hydrolases / Q000302:isolation & purification / Q000378:metabolism*; D010761:Phosphorus Radioisotopes; D051381:Rats; D013403:Sugar Phosphates / Q000378:metabolism*; D014316:Tritium
D007295:Inositol Phosphates; D010761:Phosphorus Radioisotopes; D013403:Sugar Phosphates; D014316:Tritium; C045537:inositol 4-phosphate; C052128:inositol 3-phosphate; C044259:inositol 1,4-bis(phosphate); D015544:Inositol 1,4,5-Trisphosphate; D010744:Phosphoric Monoester Hydrolases; C053087:inositol-1,4-bisphosphate 1-phosphatase