Sulphation and the vegetative growth of Dictyostelium discoideum

The utilization of [35S]sulphate by bacterially grown amoebae of Dictyostelium discoideum strain NP73 was examined in this study. During vegetative growth the sulphation of at least ten macromolecules was observed. These macromolecules had molecular masses less than 66 kDa and isoelectric points below 5. Simple tests indicated that the sulphate linkage was periodate-sensitive but not acid-labile which implied that carbohydrate moieties, rather than tyrosine residues, were sulphated. Pulse-chase experiments indicated that the sulphated macromolecules were extremely stable during vegetative growth, but that secretion occurred on starvation, resulting in the loss of the sulphated macromolecules to the extracellular medium. Incorporation of [35S]sulphate into these macromolecules by amoebae declined rapidly within 2 h of starvation on membrane filters. In contrast, incorporation by amoebae starving in suspension culture continued for 6-8 h. Similar patterns of [35S]sulphate incorporation were observed for two other strains of D. discoideum (strains AX2 and NC4) and for Polysphondylium violaceum. Since in a previous study it was shown that the sulphation inhibitor, sodium selenate, arrests the growth of D. discoideum [Davis, S.J. & Wheldrake, J.F. (1985) FEMS Micro Lett. 30, 353-358], it is suggested that the sulphation of these macromolecules is necessary for the vegetative growth of D. discoideum.