Gangliosides as Differential Modulators of Protein Phosphorylation
Gangliosides elicited complex effects on in vitro protein phosphorylation in rat brain membrane preparations. Gangliosides stimulated the phosphorylation of several phosphoproteins in brain membrane in a pattern qualitatively similar to calmodulin. The stimulation was completely dependent on the presence of Ca++. Di- and tri-sialogangliosides were more effective in stimulating phosphorylation. Gangliosides also inhibited the phosphorylation on a 78K protein in brain membrane and the myeline basic proteins in purified myelin preparations. Inhibition appeared to be an effect on C-kinase. GT1b was the most effective inhibitor of myelin basic protein phosphorylation. The results indicate that gangliosides may be the first physiological agents which can differentiate between C-kinase and calmodulin-dependent kinase.