title: Rat liver and lung mitochondria do not incorporate radioactivity from glycerol-3-phosphate or CDP-choline into glycero-3-phosphocholine.
abstract: The proposed formation of glycero-3-phosphocholine (GPC) from glycerol-3-phosphate (GP) and CDP-choline catalysed by the enzyme GPC-synthetase has been examined in liver and lung subcellular fractions. Previous observations on the incorporation of radioactive GP into the GPC-spot on paper chromatograms have been interpreted as evidence for the GPC-dependent synthesis of phosphatidylcholine. Although we could reproduce this incorporation of GP, we could not detect any incorporation of radioactive CDP-choline into the GPC-spot using the same paper chromatographic system. TLC separation of the substrate and products showed no detectable formation of GPC with either radioactive substrate. These results strongly suggest that the previously reported formation of GPC in liver and lung was due to an inaccurate identification of the true radioactive products. We demonstrate that the major radioactive product formed in liver mitochondria is glucose. A small amount of radioactive glycerol was also detected. Lung mitochondria incorporate radioactive GP into glycerol and into another unidentified compound or compounds. It is concluded that the occurrence of the GPC dependent formation of phosphatidylcholine is unlikely.
authors.affiliation: Department of Biochemistry, University of Western Ontario, London, Canada.
authors.forename: R A
authors.initials: RA
authors.lastname: Veldhuizen
authors.forename: W
authors.initials: W
authors.lastname: Thompson
authors.forename: F
authors.initials: F
authors.lastname: Possmayer
mesh_terms: D000818:Animals; D002854:Chromatography, Paper; D003566:Cytidine Diphosphate Choline / Q000378:metabolism*; D005947:Glucose / Q000096:biosynthesis; D005990:Glycerol / Q000378:metabolism; D005994:Glycerophosphates / Q000378:metabolism*; D005997:Glycerylphosphorylcholine / Q000096:biosynthesis*; D066298:In Vitro Techniques; D008168:Lung / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D008930:Mitochondria, Liver / Q000378:metabolism*; D019884:Nitrogenous Group Transferases; D051381:Rats; D014166:Transferases / Q000378:metabolism
chemical_list: D005994:Glycerophosphates; D003566:Cytidine Diphosphate Choline; D005997:Glycerylphosphorylcholine; C029620:alpha-glycerophosphoric acid; D014166:Transferases; D019884:Nitrogenous Group Transferases; C050703:sn-glycerol-3-phosphorylcholine synthetase; D005947:Glucose; D005990:Glycerol