Document Detail

CMP activates reversal of phosphatidylinositol synthase and base exchange by distinct mechanisms in rat pituitary GH3 cells.
MedLine Citation:
PMID:  2176479     Owner:  NLM     Status:  MEDLINE    
CMP is known to activate phosphatidylinositol (PtdIns)/inositol (Ins) base exchange and has been reported to activate reversal of PtdIns synthase also. Because it is possible that PtdIns synthase acting in the reverse direction, followed by re-incorporation of ambient Ins, could be responsible for base-exchange activity, we characterized these processes in rat pituitary GH3 cells. In permeabilized GH3 cells prelabelled with [3H]Ins and incubated in buffer with LiCl but without added Ins, CMP stimulated rapid accumulation of [3H]Ins and decreases in [3H]PtdIns; the Km for CMP was 1.7 mM. CDP and CTP were less effective, whereas 2'-CMP, 3'-CMP, other nucleoside monophosphates and cytidine did not influence this process. In permeabilized cells prelabelled to isotopic equilibrium with [3H]Ins and [32P]Pi, CMP stimulated decreases in both the 32P and 3H labelling of PtdIns, but did not increase that of [32P]phosphatidic acid. These findings demonstrate that in the absence of added Ins the effect of CMP is not via activation of base exchange nor via a phospholipase D, but by reversal of PtdIns synthase. In permeabilized cells prelabelled with [3H]Ins and [32P]Pi, unlabelled Ins inhibited loss of 32P labelling of PtdIns caused by CMP while markedly stimulating loss of 3H labelling of PtdIns and release of [3H]Ins. These data demonstrate that Ins inhibits reversal of PtdIns synthase, but stimulates base exchange. We conclude that in GH3 cells reversal of PtdIns synthase and PtdIns/Ins base exchange are both stimulated by CMP, but are distinct processes.
A B Cubitt; M C Gershengorn
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  The Biochemical journal     Volume:  272     ISSN:  0264-6021     ISO Abbreviation:  Biochem. J.     Publication Date:  1990 Dec 
Date Detail:
Created Date:  1991-02-14     Completed Date:  1991-02-14     Revised Date:  2009-11-18    
Medline Journal Info:
Nlm Unique ID:  2984726R     Medline TA:  Biochem J     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  813-6     Citation Subset:  IM    
Department of Medicine, Cornell University Medical College, New York, NY.
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MeSH Terms
CDP-Diacylglycerol-Inositol 3-Phosphatidyltransferase
Cell Line
Cytidine / pharmacology
Cytidine Diphosphate / pharmacology
Cytidine Monophosphate / pharmacology*
Cytidine Triphosphate / pharmacology
Inositol / metabolism
Magnesium / pharmacology
Membrane Proteins
Phosphorus Radioisotopes
Phosphotransferases / metabolism*
Pituitary Neoplasms
Transferases (Other Substituted Phosphate Groups)*
Grant Support
Reg. No./Substance:
0/Membrane Proteins; 0/Phosphorus Radioisotopes; 10028-17-8/Tritium; 63-37-6/Cytidine Monophosphate; 63-38-7/Cytidine Diphosphate; 65-46-3/Cytidine; 65-47-4/Cytidine Triphosphate; 6917-35-7/Inositol; 7439-95-4/Magnesium; EC 2.7.-/Phosphotransferases; EC 2.7.8.-/Transferases (Other Substituted Phosphate Groups); EC 3-Phosphatidyltransferase; EC protein, rat

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