Accumulation of [3H]-inositol into inositol polyphosphates during development of Dictyostelium

Inositol hexakisphosphate (InsP6) is present in large amounts during the development of Dictyostelium discoideum although its function is unknown. We have investigated the accumulation of [3H]-labelled inositol into both InsP6 and a more highly charged inositol species called InsPY during development of amoebae on filters. We report that the pattern of [3H]-labelled inositol incorporation into InsP6 and InsPY differs markedly from the pattern seen for inositol phospholipids and inositol(1,4,5)trisphosphate. Incorporation into PtdIns, PtdInsP, PtdInsP2 and Ins(1,4,5)P3 reached plateau values within 4 h. In contrast, incorporation into InsP6 continued in an approximately linear manner for the first eight hours of development. No incorporation into InsPY was seen during the first three hours of development at which time accumulation of [3H] continued linearly in a similar manner as for InsP6. Because the total cell concentration of InsP6 (measured by chemical assay) changes very little during development it seems probable that incorporation of label into InsPY after 3 h is due to a developmentally controlled metabolic switch rather than a requirement for a threshold level of its probable precursor, InsP6.