Diphosphoinositol polyphosphates: The final frontier for inositide research?

The diphosphoinositol polyphosphates comprise a group of highly phosphoryla ted compounds which have a rapid rate of metabolic turnover through tightly -regulated kinase/phosphohydrolase substrate cycles. The phosphohydrolases occur as multiple isoforms, the expression of which is apparently carefully controlled. Cellular levels of the diphosphoinositol polyphosphates are re gulated by cAMP and cGMP in a protein kinase-independent manner. These inos itides can also sense a specific mode of intracellular Ca2+ pool depletion. In this review, we will argue that these are characteristics of highly sig nificant cellular molecules.