EVIDENCE THAT BINDING OF CTP - PHOSPHOCHOLINE CYTIDYLYLTRANSFERASE TOMEMBRANES IN RAT HEPATOCYTES IS MODULATED BY THE RATIO OF BILAYER-FORMING TO NON-BILAYER-FORMING LIPIDS

Citation
H. Jamil et al., EVIDENCE THAT BINDING OF CTP - PHOSPHOCHOLINE CYTIDYLYLTRANSFERASE TOMEMBRANES IN RAT HEPATOCYTES IS MODULATED BY THE RATIO OF BILAYER-FORMING TO NON-BILAYER-FORMING LIPIDS, Biochemical journal, 291, 1993, pp. 419-427
Citations number
43
Categorie Soggetti
Biology
Journal title
ISSN journal
02646021
Volume
291
Year of publication
1993
Part
2
Pages
419 - 427
Database
ISI
SICI code
0264-6021(1993)291:<419:ETBOC->2.0.ZU;2-0
Abstract
The mechanism by which phospholipase C (PLC) digestion of cultured cel ls mediates binding of CTP:phosphocholine cytidylyltransferase to cell ular membranes was investigated. Incubation of choline-depleted rat he patocyes with PLC caused a translocation of enzyme from cytosol to mem branes concomitant with a decrease in the concentration of phosphatidy lcholine with no effect on the concentration of other phospholipids. R emoval of PLC and supplementation with choline restored the amount of phosphatidylcholine in the cells and translocated cytidylyltransferase to the cytosol. However, when phosphatidylcholine levels were decreas ed by incubation with phospholipase A2 (PLA2), there was no significan t redistribution of cytidylyltransferase activity. With PLA2 the conce ntration of phosphatidylethanolamine, as well as of phosphatidylcholin e, was significantly decreased. Since PLC, but not phospholipase A2, r aised the cellular concentration of diacylglycerol, possibly diacylgly cerol mediated the binding of cytidylyltransferase to membranes. This possibility was examined, but is unlikely, since addition of lysophosp hatidylcholine to PLC-treated cells restored the concentration of phos phatidylcholine and released cytidylyltransferase into the cytosol, bu t did not lower diacylglycerol levels to normal values. Studies in vit ro, incubations of cells with choline analogues and a survey of the li terature suggested that the over-riding common factor in regulation of cytidylyltransferase binding to membranes may be the ratio of bilayer to non-bilayer lipids in that membrane.