CHARACTERIZATION OF PHOSPHOLIPASE-ACTIVITY IN DICTYOSTELIUM-DISCOIDEUM - IDENTIFICATION OF A CA2+-DEPENDENT POLYPHOSPHOINOSITIDASE-SPECIFIC PHOSPHOLIPASE-C

We have identified a Ca2+-dependent polyphosphoinositide-specific phospholipase C activity in Dictyostelium discoideum. Addition of Ca2+ (20-mu-m) results in the rapid formation of Ins(1,4.5)P3 within 5 s and leads to sustained inositol phosphate production for up to 40 min in membranes prepared from [H-3]inositol-labelled cells. The phospholipase C activity is primarily membrane-bound under the conditions used to lyse the cells. In addition to this activity we also identified a family of Ca2+-regulated phospholipase activities active on a range of phospholipid substrates. using [H-3]palmitate labelling. Inositol-specific phospholipase C activity is highest in vegetatively growing cells and in starved cells during the first 6 h in development. during which time Ca2+ elicited a 5-fold stimulation of inositol phosphate formation. After this time, total activity decreased progressively until 15 h, after which the activity remained constant up until 24 h. During this period, Ca2+ was able to stimulate a 2-fold increase in inositol phosphates.