Biosynthesis of phosphatidylcholine by enzyme preparations from spinach leaves
1971
K.A. DEVOR | J.R. MUDD
The enzymic incorporation of choline-1,2-14C from CDP-choline-1,2-14C into phosphatidylcholine by spinach leaf preparations was characterized.The enzyme catalyzing the incorporation, choline phosphotransferase, had a pH optimum of about 8.0 and required either Mn2+ or Mg2+ as cofactor. The saturation concentration of Mn2+ was 0.3 mm and that for Mg2+ was 13 mm. The Km, for CDP-choline was 10 μm;. The choline phosphotransferase. was inhibited by sulfhydryl reagents. The enzyme was inactivated at 30°C, but this inactivation could be prevented by dithiothreitol and Mn2+. Preincubation of the enzyme with Mn2+ prevented inhibition by sulfhydryl reagents. The incorporation of diglyceride-U-14C into phosphatidylcholine was also studied. The enzyme did not show any diglyceride specificity when exogenous diglyceride was added, indicating that fatty acid distribution in phosphatidylcholine of spinach is not controlled by choline phosphotransferase.
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