Glycerophosphocholine metabolism in higher plant cells. Evidence of a new glyceryl-phosphodiester phosphodiesterase.
Glycerophosphocholine (GroPCho) is a diester that accumulates in different physiological processes leading to phospholipid remodeling. However, very little is known about its metabolism in higher plant cells. (31)P-Nuclear magnetic resonance spectroscopy and biochemical analyses performed on carrot (Daucus carota) cells fed with GroPCho revealed the existence of an extracellular GroPCho phosphodiesterase. This enzymatic activity splits GroPCho into sn-glycerol-3-phosphate and free choline. In vivo, sn-glycerol-3-phosphate is further hydrolyzed into glycerol and inorganic phosphate by acid phosphatase. We visualized the incorporation and the compartmentation of choline and observed that the major choline pool was phosphorylated and accumulated in the cytosol, whereas a minor fraction was incorporated in the vacuole as free choline. Isolation of plasma membranes, culture medium, and cell wall proteins enabled us to localize this phosphodiesterase activity on the cell wall. We also report the existence of an intracellular glycerophosphodiesterase. This second activity is localized in the vacuole and hydrolyzes GroPCho in a similar fashion to the cell wall phosphodiesterase. Both extra- and intracellular phosphodiesterases are widespread among different plant species and are often enhanced during phosphate deprivation. Finally, competition experiments on the extracellular phosphodiesterase suggested a specificity for glycerophosphodiesters (apparent K(m) of 50 microM), which distinguishes it from other phosphodiesterases previously described in the literature.
van der Rest
Benoît
B
Laboratoire de Physiologie Cellulaire Végétale, Unité Mixte de Recherche 5019, Commissariat à l'Energie Atomique, Centre National de la Recherche Scientifique, Université Joseph Fourier, Département de Biologie Moléculaire et Structurale, Grenoble, France.
Boisson
Anne-Marie
AM
Gout
Elisabeth
E
Bligny
Richard
R
Douce
Roland
R
D002247:Carbon Isotopes; D002473:Cell Wall / Q000201:enzymology; D002478:Cells, Cultured; D002794:Choline / Q000378:metabolism; D003600:Cytosol / Q000201:enzymology; D005997:Glycerylphosphorylcholine / Q000378:metabolism*; D006426:Hemicholinium 3 / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D009682:Magnetic Resonance Spectroscopy; D010710:Phosphates / Q000494:pharmacology; D010727:Phosphoric Diester Hydrolases / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*; D010759:Phosphorus Isotopes / Q000378:metabolism; D059828:Plant Cells; D010944:Plants / Q000201:enzymology*; D011523:Protoplasts / Q000201:enzymology; D013379:Substrate Specificity; D014617:Vacuoles / Q000201:enzymology
D002247:Carbon Isotopes; D010710:Phosphates; D010759:Phosphorus Isotopes; D006426:Hemicholinium 3; D005997:Glycerylphosphorylcholine; D010727:Phosphoric Diester Hydrolases; C038133:glycerophosphodiester phosphodiesterase; D002794:Choline