Stimulation of cyclic adenosine 3′,5′-monophosphate-dependent protein kinase with brain gangliosides

The holoenzyme of cAMP-dependent protein kinase (cAMP-kinase) partially purified from the particulate fraction of rat brain was stimulated by gangliosides. Among various gangliosides tested, GM 1 was most potent, giving K_a value of 19.5 μM. The maximal activation of the kinase was obtained with 100 μM GM 1 using kemptide as substrate. Gangliosides inhibited the kinase activity of the catalytic subunit of cAMP-kinase. Of various substrates tested, the ganghoside-stimulated cAMP-kinase could phosphorylate microtubule-associated protein 2, synapsin I and myelin basic protein, but not histone H 1 and casein. The molecular mechanisms of the stimulatory effect of gangliosides were investigated. The kinase activated with GM 1 was inhibited by the addition of PKItide, a specific inhibitor for cAMP-kinase. However, GM 1 did not dissociate the holoenzyme into the catalytic and regulatory subunits and did not interfere with the binding ability of cAMP to the holoenzyme. These results suggest that the gangliosides can directly activate cAMP-kinase in a different manner from cAMP.