Stimulation of hepatic phosphatidylcholine biosynthesis in rats fed a high cholesterol and cholate diet correlates with translocation of CTP: phosphocholine cytidylyltransferase from cytosol to microsomes.
A new model system for the study of phosphatidylcholine biosynthesis is presented. Young rats were fed a diet that contained 5% cholesterol and 2% cholate. After 6 days there was a 2-fold increase in the concentration of plasma phospholipid (243 mg/dl compared to 132 mg/dl for control animals) and a 3-fold increase in the concentration of plasma phosphatidylcholine. The rate of phosphatidylcholine biosynthesis was measured after injection of [Me-3H]choline into the portal veins. The incorporation of tritium into choline, phosphocholine and betaine by liver was similar for experimental and control animals, whereas there was a 3-fold increased incorporation into phosphatidylcholine of the cholesterol/cholate-fed rats. The activities of the enzymes of phosphatidylcholine biosynthesis in cytosol and microsomes were assayed. The only change detected was in the cytosolic and microsomal activities of CTP: phosphocholine cytidylyltransferase which were increased more than 2-fold in specific activity. When total cytidylyltransferase activity per liver was determined, a dramatic translocation of the enzyme to microsomes was observed. The control livers had 24% of the cytidylyltransferase activity associated with microsomes, whereas this value was 61% in the livers from cholesterol/cholate-fed rats. When the cytosolic cytidylyltransferase was assayed in the presence of phospholipid, the enzyme was stimulated several-fold and the difference in specific activity between control and cholesterol/cholate-fed rats was abolished. The increased activity in cytosol appears to be the result of a 2-fold increase in the amount of phospholipid in the cytosol from cholesterol/cholate-fed rats. The data strongly support the hypothesis that the special diet stimulates phosphatidylcholine biosynthesis by causing a translocation of the cytidylyltransferase from cytosol to microsomes where it is activated.
D000818:Animals; D001692:Biological Transport; D002791:Cholesterol, Dietary / Q000494:pharmacology*; D002793:Cholic Acids / Q000494:pharmacology*; D019916:Choline-Phosphate Cytidylyltransferase; D003600:Cytosol / Q000201:enzymology; D005260:Female; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D008862:Microsomes, Liver / Q000201:enzymology; D009713:Nucleotidyltransferases / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000096:biosynthesis*; D051381:Rats; D011919:Rats, Inbred Strains
D002791:Cholesterol, Dietary; D002793:Cholic Acids; D010713:Phosphatidylcholines; D009713:Nucleotidyltransferases; D019916:Choline-Phosphate Cytidylyltransferase