title: Phosphatidylinositol synthase of Tetrahymena: inositol isomers as substrates in phosphatidylinositol biosynthesis and headgroup exchange reactions.
abstract: Phosphatidylinositol (PtdIns) synthase in microsomal fractions derived from Tetrahymena vorax was studied to determine its activity requirements. The suitability of inositol isomers as substrates for the synthase and in headgroup exchange reactions also was investigated. Tetrahymena PtdIn synthase activity was optimum in the presence of 2 mM MgCl2 plus 2 mM MnCl2, a pH of 7.8, and a temperature of 30 degrees C. The enzyme retained approximately 80% of its activity after incubation at 70 degrees C for 10 min. PtdIns headgroup exchange activity was maximal in the presence of cytidine monophosphate. By following either the accumulation of radiolabeled reaction products or the loss of radiolabel from precursors, each of the inositol isomers tested appeared to serve as substrates for both the PtdIns synthase and PtdIns:inositol phosphatidyl transferase activities. In each case, myo-inositol and scyllo-inositol were the preferred substrates. The data suggest two routes for the formation of phosphatidyl-non-myo-inositols in Tetrahymena and the potential for the production of novel, non-myo-inositol-containing second messengers.
authors.affiliation: Department of Biology, The University of West Florida, Pensacola, Florida 32514, USA.
authors.forename: Bridget M
authors.initials: BM
authors.lastname: Riggs
authors.forename: Tanya A
authors.initials: TA
authors.lastname: Lansley
authors.forename: Phillip E
authors.initials: PE
authors.lastname: Ryals
mesh_terms: D000818:Animals; D051607:CDP-Diacylglycerol-Inositol 3-Phosphatidyltransferase / Q000378:metabolism*; D002712:Chlorides / Q000494:pharmacology; D003568:Cytidine Monophosphate / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D007294:Inositol / Q000737:chemistry / Q000378:metabolism; D015636:Magnesium Chloride / Q000494:pharmacology; D017895:Manganese Compounds / Q000494:pharmacology; D015394:Molecular Structure; D010716:Phosphatidylinositols / Q000737:chemistry / Q000378:metabolism*; D013237:Stereoisomerism; D013379:Substrate Specificity; D013696:Temperature; D013768:Tetrahymena / Q000201:enzymology*; D014166:Transferases / Q000378:metabolism
chemical_list: D002712:Chlorides; D017895:Manganese Compounds; D010716:Phosphatidylinositols; D015636:Magnesium Chloride; D007294:Inositol; D014166:Transferases; D051607:CDP-Diacylglycerol-Inositol 3-Phosphatidyltransferase; D003568:Cytidine Monophosphate; C025340:manganese chloride