Inositol phosphates: synthesis and degradation.

phospholipase C; these topics are not considered here. This review describes the pathways and enzymes for the metabolism of inositol phosphates. myo-Inositol has six hydroxyl groups that can be substi- tuted with phosphate groups (Fig. 1). There are 63 different possible myo-inositol phosphates plus the three known ino- sitol cyclic phosphates, yielding a total of 66 possible com- pounds. Thus far, nearly 20 different inositol phosphates have been detected in one or more cell types. Many early reports describe separation of inositol mono-, bis-, and trisphosphates by step gradient elution from anion exchange resins tacitly assuming that nonspecific phosphatases acted on these com- pounds. Recent studies demonstrate that the inositol phos- phates, in fact, are metabolized by highly specific kinases and phosphatases. The complexity of the pathways for formation and degradation of these compounds leads us to speculate *