Glycerylphosphorylcholine phosphodiesterase in rat liver. Subcellular distribution and localization in plasma membranes.
1. A simple new assay for glycerylphosphorylcholine phosphodiesterase is described, in which radioactive glycerylphosphorylcholine is used as substrate and the reaction products are separated by adsorption on an anion-exchange resin. 2. Rat liver subcellular fractions contained both particulate (58%) and soluble (42%) glycerylphosphorylcholine phosphodiesterase. Both activities released free choline from glycerylphosphorylcholine. 3. The particulate glycerylphosphorylcholine phosphodiesterase was recovered mainly in the nuclear and microsomal fractions and showed a distribution similar to those of 5'-nucleotidase and alkaline phosphodiesterase I, both of which are constituents of the liver plasma membrane. 4. During purification of plasma membranes glycerylphosphorylcholine phosphodiesterase, 5'-nucleotidase and alkaline phosphodiesterase I showed largely similar behaviour, indicating that glycerylphosphorylcholine phosphodiesterase is also localized in liver plasma membranes. Slight differences in the distributions of these three enzymes in density-gradient separations are discussed in relation to the possibility that they are unevenly distributed on different areas of the cell surface. 5. The differences between glycerylphosphorylcholine phosphodiesterase and alkaline phosphodiesterase I indicate that these two activities are not functions of a single enzyme. 6. The glycerylphosphorylcholine phosphodiesterase of liver plasma membranes has a pH optimum of 8.5 and a K(m) for glycerylphosphorylcholine of 0.95mm. It is inhibited by EDTA and fully reactivated by a variety of bivalent cations (and Fe(3+)).
D000818:Animals; D002413:Cations, Divalent; D002462:Cell Membrane / Q000201:enzymology*; D002467:Cell Nucleus / Q000201:enzymology; D002794:Choline; D002852:Chromatography, Ion Exchange; D004492:Edetic Acid / Q000494:pharmacology; D005997:Glycerylphosphorylcholine; D006863:Hydrogen-Ion Concentration; D008099:Liver / Q000166:cytology / Q000201:enzymology*; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology; D009708:Nucleotidases / Q000032:analysis; D010727:Phosphoric Diester Hydrolases / Q000032:analysis*; D051381:Rats; D013347:Subcellular Fractions / Q000201:enzymology
D002413:Cations, Divalent; D005997:Glycerylphosphorylcholine; D004492:Edetic Acid; D009708:Nucleotidases; D010727:Phosphoric Diester Hydrolases; D002794:Choline