Gangliosides inhibit phospholipid‐sensitive Ca²⁺‐dependent kinase phosphorylation of rat myelin basic proteins

Gangliosides inhibit the phosphorylation of both small and large rat myelin basic proteins (SMBP, LMBP) by an endogenous phospholipid‐sensitive Ca²⁺‐dependent protein kinase (C‐Kinase). Using a rat brain myelin preparation in an in vitro phosphorylation assay system, we determined the inhibition constants (IC₅₀'s) of the gangliosides G_M1, G_D1a, G_D1b, and G_T1b to be approximately 160 μM, 65 μM, 65 μM, and 40 μM, respectively. Asialoganglioside G_A1, ceramide, and Nacetylneuraminic acid (NANA, sialic acid) failed to produce similar inhibition, suggesting that both the lipid and the sialic acid moieties are necessary, but neither alone is sufficient to produce inhibition. The results indicate that gangliosides may regulate protein kinase C activities in the nervous system.