Modulation of inositol phospholipid metabolism by polyamines.
At low concentrations of Mg2+, incorporation of 32P from [gamma-32P]ATP into phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2) in plasma membranes isolated from human polymorphonuclear leucocytes was enhanced 2-4-fold by the polyamines spermidine and spermine. Polyamines had no effects on inositol phospholipid phosphorylation at high concentrations of Mg2+. At 1 mM-Mg2+, [32P]PIP2 synthesis was maximally enhanced by 2 mM-spermine and 5 mM-spermidine, whereas putrescine only slightly enhanced synthesis. Spermine decreased the EC50 (concn. for half-maximal activity) for Mg2+ in [32P]PIP2 synthesis from 5 mM to 0.5 mM. Spermine did not modulate the Km for ATP for [32P]PIP or [32P]PIP2 synthesis. Spermine also decreased the EC50 for PI in [32P]PIP synthesis. In contrast, spermine elevated the apparent Vmax, without affecting the EC50 for PIP, for [32P]PIP2 synthesis. Spermine and spermidine also inhibited the hydrolysis of [32P]PIP2 by phosphomonoesterase activity. Therefore polyamines appear to activate inositol phospholipid kinases by eliminating the requirements for super-physiological concentrations of Mg2+. Polyamine-mediated inhibition of polyphosphoinositide hydrolysis would serve to potentiate further their abilities to promote the accumulation of polyphosphoinositides in biological systems.
Smith
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Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC 27710.
Snyderman
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D019870:1-Phosphatidylinositol 4-Kinase; D002462:Cell Membrane / Q000187:drug effects; D019852:Diacylglycerol Kinase; D006801:Humans; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D015636:Magnesium Chloride; D008563:Membrane Lipids / Q000097:blood*; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000097:blood*; D010744:Phosphoric Monoester Hydrolases / Q000097:blood; D010766:Phosphorylation; D010770:Phosphotransferases / Q000097:blood; D017853:Phosphotransferases (Alcohol Group Acceptor); D011073:Polyamines / Q000494:pharmacology*; D013096:Spermine / Q000494:pharmacology; D000099182:Phosphoinositide 5-Phosphatases
D019870:1-Phosphatidylinositol 4-Kinase; D019852:Diacylglycerol Kinase; D008274:Magnesium; D015636:Magnesium Chloride; D008563:Membrane Lipids; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D010744:Phosphoric Monoester Hydrolases; D010770:Phosphotransferases; D017853:Phosphotransferases (Alcohol Group Acceptor); D011073:Polyamines; D013096:Spermine; D000099182:Phosphoinositide 5-Phosphatases; C037178:phosphatidylinositol 4-phosphate; C020077:1-phosphatidylinositol-4-phosphate 5-kinase