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Department of Biology, University of Essex, Colchester, U.K.

ABSTRACT

The intracellular phosphate concentration decreases markedly during differentiation and this decrease is unaffected by the growth conditions of the myxamoebae. Paralleling the decrease in total phosphate there is, in cells containing a high initial glycogen content, a decrease in intracellular orthophosphate. Cells not containing a high initial glycogen content show little or no change in intracellular orthophosphate until terminal stages of differentiation, when this pool rises. Since both sets of cells undergo the same morphogenetic sequence, it is unlikely that changes in intracellular orthophosphate regulate the nature of the developmental processes. Cells containing a high glycogen content initially have larger amounts of polyphosphate than those containing a low glycogen content, and whereas there is a net decrease in polyphosphate during the differentiation of the former cells there is a net increase in polyphosphate content of the latter. This makes it unlikely that the metabolic energy derived from glycogen oxidation is used to synthesise polyphosphate whose metabolic role is likely therefore to be as a phosphate store, not an energy store.