title: Ca2+ regulation of 1-(3-sn-phosphatidyl)-1D-myo-inositol 4-phosphate formation and hydrolysis on sarcoplasmic-reticular Ca2+-transport ATPase. A new principle of phospholipid turnover regulation.
abstract: Lipid phosphorylation was shown to occur on the isolated sarcoplasmic-reticulum (SR) Ca2+-transport ATPase. More than 95% of the radioactivity incorporated on incubation of the SR ATPase with [gamma-32P]ATPMg can be extracted with acidic organic solvents and was identified as 1-(3-sn-phosphatidyl)-1D-myo-inositol 4-phosphate (PtdIns4P) [Varsányi, Toelle, Heilmeyer, Dawson & Irvine (1983) EMBO J. 2, 1543-1548]. This lipid phosphorylation is only observed at nanomolar concentrations of free Ca2+; in the presence of micromolar free Ca2+ PtdIns4P disintegrates rapidly. Also, upon blockade of the kinase reaction PtdIns4P decomposes, indicating a PtdIns/PtdIns4P turnover. The PtdIns4P concentration is dependent on the free Ca2+ concentration, being half-maximal at 35 nM-Ca2+. PtdIns4P hydrolysis is catalysed by a PtdIns4P phosphomonoesterase; accordingly no diacylglycerol is formed, which would be a product of a phosphodiesteratic cleavage. Fluoride inhibits this phosphomonoesterase. Ca2+ does not influence directly either the PtdIns kinase or the PtdIns4P phosphomonoesterase. PtdIns4P forms a tight complex with the transport ATPase, from which it can be removed only by chromatography on heparin-agarose in the presence of Triton X-100. It is concluded that Ca2+ regulates the PtdIns/PtdIns4P turnover by availability of substrate, depending on the Ca2+-transport-ATPase conformation, which traps or exposes the respective lipid head groups.
authors.affiliation: Lehrstuhl für Physiologische Chemie, Ruhr-Universität Bochum, Federal Republic of Germany.
authors.forename: M
authors.initials: M
authors.lastname: Schäfer
authors.forename: G
authors.initials: G
authors.lastname: Behle
authors.forename: M
authors.initials: M
authors.lastname: Varsányi
authors.forename: L M
authors.initials: LM
authors.lastname: Heilmeyer
mesh_terms: D019870:1-Phosphatidylinositol 4-Kinase; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002847:Chromatography, Agarose; D002852:Chromatography, Ion Exchange; D005459:Fluorides / Q000494:pharmacology; D006868:Hydrolysis; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000096:biosynthesis / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D010770:Phosphotransferases / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism
chemical_list: D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D010743:Phospholipids; C037178:phosphatidylinositol 4-phosphate; D010770:Phosphotransferases; D019870:1-Phosphatidylinositol 4-Kinase; D010744:Phosphoric Monoester Hydrolases; C053153:phosphatidylinositol-3,4-bisphosphate 4-phosphatase; D000252:Calcium-Transporting ATPases; D005459:Fluorides; D002118:Calcium