Bimodal regulation of protein phosphorylation by a ganglioside in rat brain membrane

Whether or not a ganglioside influences the protein phosphorylation in the rat brain membrane fraction was investigated. Phosphorylation of the 72 kDa protein was significantly affected by the addition of 80 nM GQ1b in vitro, which is far below the reported concentration of gangliosides that affects protein phosphorylation in the neuronal membrane fraction. This action of GQ1b was bimodal: it being not only stimulatory as to the incorporation of phosphate into the 72 kDa protein on incubation of 20 sec, but also as to the release of phosphate from or breakdown of the 72 kDa protein on incubation for more than 5 min. Eighty nM GQ1b did not noticeably affect ATPase in the same fraction. These results suggest that the transphosphorylation of the 72 kDa protein is affected by the interaction of GQ1b with either the responsible enzymes or the 72 kDa protein as a substrate.