Localization of glycogen phosphorylase in specific cell types during differentiation of Dictyostelium discoideum

The localization of glycogen phosphorylase was studied during the differentiation of prespore and prestalk cells in Dictyostelium discoideum. Ultramicrotechniques were utilized to assay the enzyme activity in cell samples as small as 0.02 μg dry wt in reaction volumes of 0.1 μl. The activity was assayed using an amplification procedure employing the enzymatic cycling of pyridine nucleotides. Glycogen phosphorylase from individual organisms was assayed during the developmental period. Early in development, activity was low but gradually increased to a maximum value at culmination. From culmination to sorocarp, enzyme activity decreased rapidly. Cell-specific assays of spores showed that phosphorylase activity increased slightly to culmination, and then decreased. Prestalk cells showed the greatest activity in the area of stalk sheath construction and elongation. Stalk cells showed a decreasing gradient of enzyme activity from the tip of the stalk to the base. Enzyme activity in the spores may be sufficient to provide glucose units for trehalose synthesis and spore coat production. The prestalk enzyme may degrade glycogen to provide glycosyl units for production of the stalk sheath and trehalose. Possible models of cell-specific biochemical events in Dictyostelium discoideum are discussed.