Phosphoinositides inositol phosphates

Metabolic regulation of phosphoinositides/inositol phosphates in response to abiotic stress... 

Furthermore, phosphoinositide/inositol phosphate turnover plays an important role in the production of secondary messengers during abiotic stress in plants. Within a few seconds, hyperosmotic shock induced a rapid and transient increase of Ins( 1,4,5)P3 in Arabidopsis cultured cells. This fact strongly suggests the PI turnover system functions near an osmosensor however, the molecule that functions as the osmosensor has not been identified, except in yeast and bacteria. In the near future, we hope to determine which molecule can activate the PI turnover system in response to hyperosmotic stress in plants. 

The inositol polyphosphate 5-phosphatases belong to a family of enzymes that terminate the signals generated by inositol lipid kinases and PLC. To date, two major types of 5-phosphatase have been identified, both of which share a common 5-phosphatase domain of approximately 300 amino acids, with several highly conserved motifs. Type-I enzymes are 43-65 kDa and preferentially hydrolyze 1(1,4,5)P3 and 1(1,3,4,5)P4, with the attendant formation of I(1,4)P2 and 1(1,3,4)P3, but have little or no activity towards membrane-bound phosphoinositides. The pro-totypic form of a type-15-phosphatase is a 43 kDa protein that is post-translationally modified by farnesylation of the carboxyl terminus CAAX motif this modification juxtaposes the enzyme with the membrane. Type-II enzymes are larger (75-160 kDa) and will hydrolyze both water-soluble inositol phosphates and lipids that... 

The action of Li+ on inositol monophosphatase has greatly facilitated the use of [3H] inositol in the study of stimulated phosphoinositide turnover [19]. Berridge and colleagues demonstrated that in the presence of both Li+ and a phosphoinositide-linked ligand, the amount of labeled intracellular inositol phosphates that accumulates... 

Volume 26 myo-Inositol Phosphates, Phosphoinositides, and Signal Transduction... 

Litosch I, Wallis C, Fain JN. 1985. 5-Hydroxytryptamine stimulates inositol phosphate production in a cell-free system from blowfly salivary glands. Evidence for a role of GTP in coupling receptor activation to phosphoinositide breakdown. J Biol Chem 260 5464-5471. 

Measurement of Phosphoinositide Turnover. As a result of these labeling experiments, two analytical procedures can be used to assess the involvement of the phosphoinositides in stimulus-induced activation of platelets by the agonist, PAF. One uses the measurement of the change in phosphoinositide levels per se as determined by [32P]phosphate labeling, and the other uses an assay to determine the accumulation of [3H]inositol phosphates through myo-[3H]inositol labeling. 

Grado, C. and Ballou, C. E. (1961) Myo-inositol phosphate obtained by alkaline hydrolysis of beef brain phosphoinositide, J. Biol. Chem. 236, 54-60. 

From the evidence accumulated so far, it seems likely that the cAMP signal transduction pathway will be a major effector of a stimulatory signal to the pars tuberalis, which can be regulated by melatonin [115]. The effect of aluminum as AlF41 has been studied on inositol phosphate accumulation, calcium mobilization, and cyclic AMP production in ovine pars tuberalis cells [116]. In the presence of 10 mmol L-1 LiCl, AlF41 stimulated the net accumulation of inositol phosphates over a 40-min incubation. Lithium is a known inhibitor of phosphatases in the inositol phosphate-recycling pathway. The results show the existence of a lithium-sensitive phosphoinositide signaling. 

Murthy, P.P.N., 1996, Metabolism of inositol phosphates in plants. In Biswas, B.B. and Biswas, S. (eds.), Inositol Phosphates, Phosphoinositides, and Signal Transduction, Subcellular Biochemistry Series, Vol. 26, Plenum Press, New York, pp. 227-255. 

Biswas, B.B., Biswas, S., Chakrabarti, S., and De, B.P., 1978a, A novel metabolic cycle involving myo-inositol phosphates during formation and germination of seeds. In Wells, W.W. and Eisenberg, E, Jr. (eds.), Cyclitols and Phosphoinositides. Academic Press, New York, pp. 57-68. 

In animal systems, it is well documented that phosphoinositides and inositol phosphates participate in various signal transduction processes. One of the most studied signaling events involved in phosphoinositide turnover is the generation... 

---