Inositide metabolism

The idea that stimulated inositide metabolism was involved in increases in cytoplasmic Ca2+ was first proposed by Bob Michell (1975). To date, over 20 different inositol phosphates can be isolated from stimulated cells, but so far only one of these molecules can be ascribed a definite function Ins 1,4,5-P3, which is released into the cytoplasm following PLC hydrolysis of PIP2, liberates Ca2+ from intracellular stores. A role for Ins 1,3,4,5-P4in opening a Ca2+ gate , thus allowing the influx of Ca2+ from the external... 

Maly, K Oberhuber, H., Doppler, W Hoflacher, J., Jaggi, R., Groner, B., Grunicke, H. (1988). Effect of H-ras on phosphatidyl inositide metabolism, Na+/H+ antiporter and intracellular calcium. Adv. Enzyme Regul. 27, 121-143. 

Poovaiah BW, Reddy ASN In Boss W, Loewus F. Morre J (eds) Inositide Metabolism in Plants. Liss, New York (in press)... 

Involvement of inositide metabolism in the transduction mechanism from receptor activation to control of cellular processes such as contraction... 

Fig. 4. Inositide metabolism initiated by binding of an agonist to a cell membrane...

Ueda, H., Kobayashi, T., Kishimoto, M., Tsutsumi, T, and Okuyama, H. (1993) A possible pathway of phosphoinositide metabolism through EDTA-insensitive phospholipase A followed by lysophospho-inositide-specific phospholipase C in rat brain. Journal of Neurochemistry 61 1874—1881. 

Phosphatidylinositol is also formed from CDP-diacylglycerol, though in this case only one enzyme step is involved (Figs 11.13 and 11.14). The higher inositides, diphosphoinositide and triphospho-inositide, are formed from phosphatidylinositol by two kinases (Fig. 11.13). These activities are particularly high in nervous tissue (Michell, 1975). Metabolism of other minor inositol-containing lipids has been reviewed (Hawthorne, 1982). 

The metabolic turnover of phosphoinositides in numerous tissues has received a great deal of attention with particular interest being focused on the polar head groups of the lipids. IThat has received comparatively little attention, however, is the fatty acid turnover and the mechanisms for regulation of the molecular species of these lipids. In a number of tissues arachidonic acid is the predominant unsaturated fatty acid of each of the inositides and in rat brain this is a unique feature of the inositides. Not only is arachidonate an important fatty acid, but it seems of importance for the cell to position arachidonate in position - 2 of the phos-phoinositide molecule. 

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