Localization of glycosyl transferases in plasma membranes from Dictyostelium discoideum

Crude membranes from vegetative and aggregation competent cells of Dictyostelium discoideum Ax 2 were separated by a combination of differential and sucrose gradient centrifugation. A fraction mainly containing plasma membranes could be isolated. The high degree of purity was demonstrated by electron microscopy and by the presence of marker enzymes typical for the plasma membrane and the absence of enzymes characteristic for other subcellular compartments. Furthermore surface labelling with radioactive 1--fluoro--2,4--dinitrobenzene--14C and cAMP binding capacity were introduced as plasma membrane markers. In the pure plasma membrane fraction endogenous activities of D--mannosyl-, D--glucosyl- and N--Acetyl--D--glucosaminyl--transferases were present. The activities in plasma membranes of aggregation competent cells were up to thirty times higher than in membranes isolated from vegetative cells.