Kinetic selectivity of cholinephosphotransferase in mouse liver: the Km for CDP-choline depends on diacylglycerol structure.
The effects of different 1,2-diacyl-sn-glycerols on the kinetic properties of CDP-choline:1,2-diacylglycerol cholinephosphotransferase (EC 2.7.8.2) from mouse liver microsomes have been studied. Initial-velocity experiments were carried out with various concentrations of several species of diacylglycerol at different fixed concentrations of CDP-choline. Kinetic analysis of these data showed a family of intersecting lines consistent with a sequential kinetic mechanism of catalysis. The Km and Vmax. values derived from rate data revealed a pronounced effect of diacylglycerol species utilization on the Km value for CDP-choline. There was a biphasic relationship between diacylglycerol chain length and the Km for CDP-choline. Substitution of an unsaturated fatty acid in the sn-2 position of distearin also dramatically increased the CDP-choline Km value as well as the Vmax. 1,2-Dipalmitoyl-sn-glycerol was the preferred substrate over other disaturated species, but 1,2-dihexanoyl-sn-glycerol could not be utilized. These results demonstrate the kinetic mechanism of in vitro catalysis and suggest a regulatory role for CDP-choline concentration in the diacylglycerol species selectivity of cholinephosphotransferase resulting in the de novo biosynthesis of different molecular species of phosphatidylcholine.
Mantel
C R
CR
Department of Medicine (Hematology/Oncology), Indiana University School of Medicine, Indianapolis.
Schulz
A R
AR
Miyazawa
K
K
Broxmeyer
H E
HE
D000818:Animals; D002384:Catalysis; D003566:Cytidine Diphosphate Choline / Q000378:metabolism*; D002798:Diacylglycerol Cholinephosphotransferase / Q000378:metabolism*; D004075:Diglycerides / Q000378:metabolism*; D005227:Fatty Acids; D005260:Female; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D051379:Mice; D008809:Mice, Inbred C3H; D013379:Substrate Specificity
D004075:Diglycerides; D005227:Fatty Acids; D003566:Cytidine Diphosphate Choline; D002798:Diacylglycerol Cholinephosphotransferase