Biomaterial Database

Metabolism of lysopolyphosphoinositides by rat brain and liver microsomes. 1986

F B Palmer

Lysophosphatidylinositol 4,5-bisphosphate has been reported to form ion-conducting channels in artificial membranes. If formed in vivo, mechanisms for its removal from cellular membranes would be required. Thus, possible pathways were explored in rat brain and liver microsomes. Since neither lysophosphatidylinositol 4-phosphate nor lysophosphatidylinositol 4,5-bisphosphate were acylated in experiments with [3H]arachidonic acid or [14C]oleoyl CoA, polyphosphoinositides do not participate directly in a deacylation-reacylation cycle as proposed for the postsynthesis enrichment of phosphatidylinositol with arachidonic acid. Similar enrichment in polyphosphoinositides can occur only via the rapid phosphorylation-dephosphorylation cycle linking all three phosphoinositides. Lysophosphatidyl[2-3H]inositol 4,5-bisphosphate and lysophosphatidyl[2-3H]inositol 4-phosphate were rapidly dephosphorylated to 1-acyl-sn-glycero(3)phospho(1)-D-myo-inositol by microsomes from both tissues. Appearance of only trace quantities of radioactive lysophosphatidylinositol monophosphate during the catabolism of lysophosphatidyl[2-3H]inositol 4,5-bisphosphate indicated that the second dephosphorylation step, which was cation independent, was at least as fast as the first step which required Mg2+. In the presence of ATP, CoA, and arachidonic acid, the lysophosphatidylinositol was converted to phosphatidylinositol. This acylation reaction was rate limiting in brain microsomes. Dephosphorylation of lysophosphatidylinositol 4,5-bisphosphate was rate limiting in liver microsomes. Neither the lysopolyphosphoinositides nor the lysophosphatidylinositol produced from them in the reactions were degraded by acyl hydrolases or phosphodiesterases in microsomes from either tissue. Therefore, any lysopolyphosphoinositide formed in vivo would probably be removed by dephosphorylation and recycled to phosphatidylinositol.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008861	Microsomes	Artifactual vesicles formed from the endoplasmic reticulum when cells are disrupted. They are isolated by differential centrifugation and are composed of three structural features: rough vesicles, smooth vesicles, and ribosomes. Numerous enzyme activities are associated with the microsomal fraction. (Glick, Glossary of Biochemistry and Molecular Biology, 1990; from Rieger et al., Glossary of Genetics: Classical and Molecular, 5th ed)	Microsome
D008862	Microsomes, Liver	Closed vesicles of fragmented endoplasmic reticulum created when liver cells or tissue are disrupted by homogenization. They may be smooth or rough.	Liver Microsomes,Liver Microsome,Microsome, Liver
D010716	Phosphatidylinositols	Derivatives of phosphatidic acids in which the phosphoric acid is bound in ester linkage to the hexahydroxy alcohol, myo-inositol. Complete hydrolysis yields 1 mole of glycerol, phosphoric acid, myo-inositol, and 2 moles of fatty acids.	Inositide Phospholipid,Inositol Phosphoglyceride,Inositol Phosphoglycerides,Inositol Phospholipid,Phosphoinositide,Phosphoinositides,PtdIns,Inositide Phospholipids,Inositol Phospholipids,Phosphatidyl Inositol,Phosphatidylinositol,Inositol, Phosphatidyl,Phosphoglyceride, Inositol,Phosphoglycerides, Inositol,Phospholipid, Inositide,Phospholipid, Inositol,Phospholipids, Inositide,Phospholipids, Inositol
D010744	Phosphoric Monoester Hydrolases	A group of hydrolases which catalyze the hydrolysis of monophosphoric esters with the production of one mole of orthophosphate.	Phosphatase,Phosphatases,Phosphohydrolase,Phosphohydrolases,Phosphomonoesterase,Phosphomonoesterases,Phosphoric Monoester Hydrolase,Hydrolase, Phosphoric Monoester,Hydrolases, Phosphoric Monoester,Monoester Hydrolase, Phosphoric
D001921	Brain	The part of CENTRAL NERVOUS SYSTEM that is contained within the skull (CRANIUM). Arising from the NEURAL TUBE, the embryonic brain is comprised of three major parts including PROSENCEPHALON (the forebrain); MESENCEPHALON (the midbrain); and RHOMBENCEPHALON (the hindbrain). The developed brain consists of CEREBRUM; CEREBELLUM; and other structures in the BRAIN STEM.	Encephalon
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D001095	Arachidonic Acids		Eicosatetraenoic Acids,Acids, Arachidonic,Acids, Eicosatetraenoic
D014316	Tritium	The radioactive isotope of hydrogen also known as hydrogen-3. It contains two NEUTRONS and one PROTON in its nucleus and decays to produce low energy BETA PARTICLES.	Hydrogen-3,Hydrogen 3
D016718	Arachidonic Acid	An unsaturated, essential fatty acid. It is found in animal and human fat as well as in the liver, brain, and glandular organs, and is a constituent of animal phosphatides. It is formed by the synthesis from dietary linoleic acid and is a precursor in the biosynthesis of prostaglandins, thromboxanes, and leukotrienes.	(all-Z)-5,8,11,14-Eicosatetraenoic acid,Arachidonic Acid, (all-Z)-Isomer, 1-(14)C-Labeled,Arachidonic Acid, (all-Z)-isomer, 3H-Labeled,Arachidonic Acid, Ammonium Salt, (all-Z)-Isomer,Arachidonic Acid, Cerium Salt, (all-Z)-Isomer,Arachidonic Acid, Cesium Salt, (all-Z)-Isomer,Arachidonic Acid, Lithium Salt, (all-Z)-Isomer,Arachidonic Acid, Potassium Salt, (all-Z)-Isomer,Arachidonic Acid, Sodium Salt,Arachidonic Acid, Sodium Salt, (all-Z)-Isomer,Arachidonic Acid, Zinc Salt, (all-Z)-Isomer,Sodium Arachidonate,Vitamin F,Arachidonate, Sodium