Human platelets incubated with [32P]Pi and [3H]arachidonate were transferred to a Pi-free Tyrode's solution by gel filtration. The labile phosphoryl groups of ATP and ADP as well as Pi in the metabolic pool of these platelets had equal specific radioactivity which was identical to that of[32P]phosphatidate formed during treatment of the cells with thrombin for 5 min. Therefore, the 32P radioact...

The addition of cyclic AMP (cAMP) to Saccharomyces cerevisiae cyr1 mutant cells resulted in an increase in the rate of phosphatidylinositol synthesis at the expense of phosphatidylserine synthesis. The decrease in phosphatidylserine synthesis correlated with the down regulation of phosphatidylserine synthase activity by cAMP-dependent protein kinase phosphorylation. The increase in phosphatidyl...

Professional phagocytic cells ingest microbial intruders by engulfing them into phagosomes, which subsequently mature into microbicidal phagolysosomes. Phagosome maturation requires sequential fusion of the phagosome with early endosomes, late endosomes, and lysosomes. Although various phosphoinositides (PIPs) have been detected on phagosomes, it remained unclear which PIPs actually govern phag...

A recent hypothesis suggests that proteolytic activity of the micromolar and millimolar Ca2+-requiring forms of the Ca2+-dependent proteinases (mu- and m-calpain, respectively) is regulated in vivo by their association with a phosphatidylinositol-containing site on the plasma membrane followed by autolysis of the proteinases. Phosphatidylinositol association lowers the Ca2+ concentration needed...

Stimulated phosphatidylinositol breakdown, followed by compensatory resynthesis, is a response of a wide variety of cells to many hormones and neurotransmitters. Until recently, most work on this response employed secretory tissues, nervous tissues or smooth muscles, and the most intensively studied stimuli were muscarinic, cholinergic and a-adrenergic. As a tentative synthesis of all of these ...

Phosphatidylinositol (PI) is a precursor for an important class of phospholipids, the phosphatidylinositol polyphosphates. Because renal myo-inositol levels may vary under both physiological (e.g., antidiuretic) and pathophysiological (e.g., diabetic) conditions, the formation of PI from CDP-diacylglycerol (CDP-DG) and myo-inositol via phosphatidylinositol synthase and the regulation of this en...