Ganglioside-modulated protein phosphorylation in muscle. Activation of phosphorylase b kinase by gangliosides.

Gangliosides have profound effects on protein phosphorylation in skeletal muscle. Addition of GT1b to guinea pig muscle extract stimulated the phosphorylation of a 98-kDa protein 4-8-fold. In contrast, Ca2+ stimulated the phosphorylation of this protein and two other proteins with apparent Mr of 107,000 and 145,000, respectively. Addition of GT1b in the presence of Ca2+ further enhanced the phosphorylation of the 98-kDa protein but completely inhibited the phosphorylation of both the 107- and the 145-kDa proteins. The nature of the ganglioside-modulated 98-kDa protein has been characterized. Results on the pH activity profiles and the requirements of Ca2+ for phosphorylation suggest that this phosphoprotein may correspond to glycogen phosphorylase. Phosphorylation of purified rabbit muscle phosphorylase b by nonactivated phosphorylase kinase was stimulated by GT1b. This stimulation was in part due to an activation of the kinase activity. Autophosphorylation of highly purified phosphorylase kinase was increased 4-10-fold in the presence of GT1b. Polysialogangliosides were more potent than monosialogangliosides in stimulating the autocatalytic activity, whereas asialo-GM1, colominic acid, N-acetylneuraminic acid, and phosphatidylserine were ineffective. The effects of gangliosides were dose-dependent. At physiological pH, the concentrations of GT1b required for half-maximal stimulation of the autophosphorylation of phosphorylase kinase were 6.4 microM in the absence of Ca2+ and 1.3 microM when the divalent cation was present. These findings suggest that gangliosides may play a role as biomodulators in the regulation of glycogenolysis in muscle.