Phosphatidylinositol cycle

FIcytidine monophosphate phosphatidic acid DAG = diacylglycerol G = G protein Glu-6-P, glucose 6-phosphate IPj = inositol monophosphate IP2 = inositol biphosphate ... 

These studies all support the hypothesis that external stimuli of the elicitor cause an increase in the cytoplasmic Ca2+ level via the phosphatidylinositol cycle and/or the adenylate cyclase system. Although an authoritative picture of this process cannot yet be given, possible signal transduction mechanisms are summarized in Fig. (2). At present the data... 

IP3 is rapidly degraded to inactive IP2 and then on to inositol. Meanwhile, diacylglycerol is phosphorylated and then converted to CDP-diacylglycerol, which combines with inositol to form phosphatidylinositol. The latter is subsequently phosphorylated in two steps to PIP2. The degradation and resynthesis of PIP2 completes the so-called phosphatidylinositol cycle. 

Grabowski, L., Heim, S., and Wagner, K.G., 1991, Rapid changes in the enzyme activities and metabolites of the phosphatidylinositol-cycle upon induction by growth substrates of auxin-starved suspension cultured Catharanthus roseus cells. Plant Sci. 75 33-38. 

LaSSING I, LINDERG U. Evidence th the phosphatidylinositol cycle is linked to cell motility. Exp Cedi Res 174 1-15,1988. 

S ATP + l-stearoyl-2-arachidonoyl-sn-glycerol <5> (<5>, since diacylglycerol kinase is an enzyme of the phosphatidylinositol cycle, its natural substrate could be l-stearoyl-2-arachidonoyl-sn-glycerol, thought to be the main diacylglycerol analog generated from phosphoinositide [7]) (Reversibility <5> [7]) [7]... 

Lithium, known to reduce the wiyo-inositol levels, blocks the induction of expression of the Tdc and Str genes by a yeast extract, whereas myoinositol counteracts the effect. The phosphate uptake was not affected by the addition of lithium. This points to the possible involvement of the phosphatidylinositol cycle in the signal-transduction pathway of the induction by elicitation (285). Also, in other cell cultures, evidence has been found for the involvement of the phosphatidylinositol cycle in elicitor-induced phytoalexin production (342,343). 

Fig. 4. The phosphatidylinositol cycle, which may yield arachidonic acid by two different mechanisms By hydrolysis of diacylglycerol or by stimulation of phospholipase A 2 activity through release of calcium by ionophore effects of phosphatidic acid. The latter can then be recycled to phosphatidylinositol. 

Atack JR, Prior AM, Fletcher SR, Quirk K, MeKcman R, Ragan Cl (1994) Effects of L-690,488, a prodrug of the bisphosphmate inositol mmophosphatase inhibitor L-690,330, on phosphatidylinositol cycle markers. J Pharmacol Exp Ther 270 70-76... 

In mammalian tissues, phospholipases C which attack inositol lipids are very important since they initiate the phosphatidylinositol cycle (section 8.8). In addition, broad-specificity phospholipases C are located in lysosomes. 

Figure 8.7 The phosphatidylinositol cycle and ancillary reactions. Abbreviations CDP-DAG = CDP-diacylglycerol ...

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