title: Cholinephosphotransferase activity in human platelets.
abstract: Disrupted human platelets possess a cholinephosphotransferase activity (EC 2.7.8.2) whose properties have been studied in this work. The labeling of choline glycerophospholipid (CGP) from radioactive cytidine-5'-diphosphate choline (CDP-choline) in vitro shows a maximum at pH 8.0 (using Hepes [4-(2-hydroxyethyl)-piperazine-1-ethane-2-sulfonic acid] as a buffer) and is stimulated by Mn2+, Mg2+ and diacylglycerol. The enzymic activity is inhibited by Ca2+. The dependence of human platelet cholinephosphotransferase upon CDP-choline concentration does not follow the Michaelis-Menten equation. CMP strongly inhibits the reaction. The functional implications of this newly discovered platelet activity are briefly considered.
mesh_terms: D001792:Blood Platelets / Q000201:enzymology*; D001798:Blood Proteins / Q000378:metabolism; D002413:Cations, Divalent / Q000494:pharmacology; D055598:Chemical Phenomena; D002621:Chemistry; D002798:Diacylglycerol Cholinephosphotransferase / Q000037:antagonists & inhibitors / Q000097:blood / Q000302:isolation & purification*; D004075:Diglycerides / Q000494:pharmacology; D004789:Enzyme Activation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D010770:Phosphotransferases / Q000302:isolation & purification*
chemical_list: D001798:Blood Proteins; D002413:Cations, Divalent; D004075:Diglycerides; D010770:Phosphotransferases; D002798:Diacylglycerol Cholinephosphotransferase