Synthesis of polyphosphoinositides in vertebrate photoreceptor membranes.
Rod outer segments isolated from bovine retinas incorporated 32P into phospholipids after incubation with [gamma-32P]ATP in a Mg2+-containing medium. Only phosphatidylinositol 4-phosphate, phosphatidylinositol 4,5-bisphosphate, and phosphatidate were labelled. The incorporation of label into lipids was detected as early as 20 s after the start of incubation and the products were stable for at least 10 min. The reactions were time, protein and ATP-concentration dependent. Entire rod outer segments showed higher diacylglycerol kinase and lower phosphatidylinositol and phosphatidylinositol 4-phosphate kinase activities than the disc membranes obtained from them. Exogenously added phosphatidylinositol (up to 1 mM) in the presence of Triton X-100 increased phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate labelling in rod outer segments (8- and 6-fold, respectively). Triton X-100 at a concentration of 0.4% stimulated phosphorylation of endogenous phosphoinositides. Diacylglycerol kinase activity was largely suppressed by the detergent, but this effect was partially reversed by addition of phosphatidylinositol. It is suggested that the rod outer segments contain phosphatidylinositol kinase and phosphatidylinositol 4-phosphate kinase bound to disc membranes, as well as an active diacylglycerol kinase occurring either as a soluble or a peripherally bound protein in disc membranes.
D019870:1-Phosphatidylinositol 4-Kinase; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002417:Cattle; D019852:Diacylglycerol Kinase; D017830:Octoxynol; D010712:Phosphatidic Acids / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000096:biosynthesis* / Q000378:metabolism; D010761:Phosphorus Radioisotopes; D010770:Phosphotransferases / Q000032:analysis; D017853:Phosphotransferases (Alcohol Group Acceptor); D010786:Photoreceptor Cells / Q000378:metabolism*; D011092:Polyethylene Glycols / Q000494:pharmacology; D012374:Rod Cell Outer Segment / Q000378:metabolism; D013997:Time Factors
D010712:Phosphatidic Acids; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D010761:Phosphorus Radioisotopes; C037178:phosphatidylinositol 4-phosphate; D011092:Polyethylene Glycols; D000255:Adenosine Triphosphate; D017830:Octoxynol; D010770:Phosphotransferases; D017853:Phosphotransferases (Alcohol Group Acceptor); D019852:Diacylglycerol Kinase; D019870:1-Phosphatidylinositol 4-Kinase; C020077:1-phosphatidylinositol-4-phosphate 5-kinase