Uptake and phosphorylation of phosphatidylinositol by rat liver nuclei. Role of phosphatidylinositol transfer protein.
The incorporation of phosphatidyl[2-3H]inositol ([3H]PI) from vesicles or microsomal membranes into rat liver nuclei is greatly stimulated by phosphatidylinositol transfer protein (PI-TP). The nuclei are able to phosphorylate [3H]PI, with the production of phosphatidylinositol 4-phosphate (PIP). Recovery of tritiated inositol trisphosphate, inositol phosphate, glycerophosphoinositol and inositol, suggests that in isolated nuclei a large set of enzymes of the PI cycle is present, similar to the enzymes involved in the plasma membrane PI cycle. Incubation with [gamma-32P]ATP shows that isolated nuclei are able to phosphorylate endogenous PI to PIP and phosphatidylinositol 4,5-bisphosphate (PIP2). In the presence of exogenous PI and detergent the synthesis of PIP is increased, indicating that in nuclei the PI pool is suboptimal for the PI-kinase activity. The present study suggests that PI-TP may be involved in providing substrates for PI metabolism at the nuclear level.
Capitani
S
S
Institute of Anatomia Umana Normale, University of Ferrara, Italy.
Helms
B
B
Mazzoni
M
M
Previati
M
M
Bertagnolo
V
V
Wirtz
K W
KW
Manzoli
F A
FA
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002458:Cell Fractionation; D002467:Cell Nucleus / Q000378:metabolism*; D002855:Chromatography, Thin Layer; D007700:Kinetics; D008081:Liposomes / Q000378:metabolism; D008099:Liver / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008565:Membrane Proteins; D010716:Phosphatidylinositols / Q000378:metabolism*; D049294:Phospholipid Transfer Proteins; D010766:Phosphorylation; D051381:Rats; D011919:Rats, Inbred Strains
D002352:Carrier Proteins; D008081:Liposomes; D008565:Membrane Proteins; D010716:Phosphatidylinositols; D049294:Phospholipid Transfer Proteins