Stimulation of cholinephosphotransferase activity by phosphatidylcholine transfer protein. Regulation of membrane phospholipid synthesis by a cytosolic protein.
The effect of rat liver phosphatidylcholine transfer protein on the incorporation of CDP-choline and dioleoylglycerol into phosphatidylcholine catalyzed by rat liver microsomal CDP-choline: 1,2-diacyl-sn-glycerol cholinephosphotransferase was studied. In the presence of phosphatidylcholine transfer protein, the incorporation of CDP-choline into phosphatidylcholine was markedly stimulated. Phosphatidylcholine transfer protein isolated from either rat or bovine liver was capable of this stimulatory effect; in contrast, phosphatidylinositol transfer protein from rat liver had no effect on phosphatidylcholine synthesis. Kinetic analysis showed that microsomal phosphatidylcholine synthesis increased 2.4-fold after 1 min and reached a maximum of approximately 10-fold within 10 min in the presence of phosphatidylcholine transfer protein; in the absence of this protein phosphatidylcholine synthesis stopped after 2-4 min. These results suggest that phosphatidylcholine transfer protein permits phosphatidylcholine synthesis to proceed further. With the addition of phospholipid vesicles, as an acceptor membrane in the reaction mixture, there was a significant amount of protein-mediated transfer of synthesized phosphatidylcholine to the vesicles. Measurable transfer of synthesized phosphatidylcholine to vesicles could only be detected after a lag of 2-4 min. The stimulation of cholinephosphotransferase could be nearly abolished by increasing the amount of added phospholipid vesicles; concurrently, a greater transfer to the vesicles was observed. These results describe a new property of phosphatidylcholine transfer protein which may be of physiological significance in the regulation of phosphatidylcholine synthesis in mammalian tissues.
Khan
Z U
ZU
Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City 66103.
Helmkamp
G M
GM
D000727:Androgen-Binding Protein; D000818:Animals; D002352:Carrier Proteins / Q000502:physiology*; D002798:Diacylglycerol Cholinephosphotransferase / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000378:metabolism*; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids / Q000378:metabolism; D010770:Phosphotransferases / Q000378:metabolism*; D060789:Prostatein; D051381:Rats; D011919:Rats, Inbred Strains; D060765:Secretoglobins; D013379:Substrate Specificity; D014598:Uteroglobin; D060788:Mammaglobin B
D000727:Androgen-Binding Protein; D002352:Carrier Proteins; D002798:Diacylglycerol Cholinephosphotransferase; D008565:Membrane Proteins; D010713:Phosphatidylcholines; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids; D010770:Phosphotransferases; D060789:Prostatein; D060765:Secretoglobins; D014598:Uteroglobin; C511484:Scgb1d2 protein, rat; C511483:Scgb1d4 protein, rat; C556468:Scgb2a1 protein, rat; D060788:Mammaglobin B