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

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Abstract
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 GQlb in vitro, which is far below the reported concentration of gangliosides that affects protein phosphorylation in the neuronal membrane fraction. This action of GQlb was bimodal: it being not only stimulatory as to the incorporation of phosphate into the 72 kDa protein on incubation for 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 GQlb 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 GQlb with either the responsible enzymes or the 72 kDa protein as a substrate.