STIMULATION OF INOSITIDE DEGRADATION IN CLUMPING STIGMATELLA-AURANTIACA

Numerous external signals which activate inositol phospholipid hydroly sis in eukaryotes are known; probably all of these signals are transdu ced by G proteins. So far, neither signal-transducing G protein nor re ceptor-regulated phospholipase C has been found in prokaryotes. Howeve r, a group of bacteria, the myxobacteria, displays cellular and tissue -like differentiation; therefore, it appeared that a search for the va rious activities involved in a signal-activated phosphatidylinositol c ycle might be rewarding. Here, we report that in Stigmatella aurantiac a, under conditions which promote clumping, inositol phospholipid synt hesis and degradation were stimulated with the resulting formation of inositol phosphate and inositol bisphosphate. The turnover was Ca2+ de pendent and was increased by fluoride ions. Membrane preparations from these cells showed a phospholipase C activity which increased with th e stage of incubation and which was stimulated by GTP gamma S, suggest ing G protein dependency. To what extent this system in a prokaryotic cell shares properties of the phosphatidylinositol cycle in eukaryotes remains unexamined.