The permeability of Dictyostelium discoideum amoebae towards amino acids and inulin was studied under conditions suitable for development of aggregationcompetence and in thick cell suspensions. During the pre-aggregation period, the amoebae released large amounts of amino acids and nucleotides into the suspending medium. The uptake of glutamate and lysine by amoebae was passive, but inulin was taken up actively, probably by pinocytosis. Hence the simplest explanation for leakage of metabolites is that the amoebae have no active mechanism for retaining them. A possible relationship between initiation of differentiation and loss of pool metabolites is discussed.

The reduction in cell surface charge density during the early stages of differentiation of the cellular slime mould, Dictyostelium discoideum, has been studied by the technique of cell electrophoresis. Using specific chemical reagents, it was shown that the cell surface negative charge was probably due to side chain carboxyl groups of proteins. During differentiation, there was a decrease in the density of these groups, accompanied by an increase in that of amino groups. The significance of this finding is discussed in relation to cell surface structure and cell differentiation.