Activation of (Na+, K+)‐ATPase by Nanomolar Concentrations of GM1 Ganglioside

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Abstract
GM1 ganglioside binding to the crude mitochondrial fraction of rat brain and its effect on (Na+, K+)-ATPase were studied, the following results being obtained: the binding process followed a biphasic kinetics with a break at 50 nM-GM1; GM1 at concentrations below the break was stably associated and over the break it was loosely associated; stably bound GM1 activated (Na+, K+)-ATPase up to a maximum of 43%; the activation was dependent upon the amount of bound GM1 and was highest at the critical concentration of 20 pmol bound GM1/mg protein; loosely bound GM1 suppressed the activating effect on (Na+, K+)-ATPase elicited by firmly bound GM1; GM1-activated (Na+, K+)-ATPase had the same pH optimum and apparent Km (for ATP) as normal (Na+, K+)-ATPase but a greater apparent Vmax; under identical binding conditions (2 h, 37.degree. C, with 40 nM substance) all tested gangliosides (GM1, GD1a, GD1b and GT1b) activated (Na+, K+)-ATPase (from 26-43%); NeuNAc [neutral nicotinic acid], sodium dodecylsulfate, sulfatide and cerebroside had only a very slight effect. The ganglioside activation of (Na+-K+)-ATPase is evidently a specific phenomenon not related to the amphiphilic and ionic properties of gangliosides, but due to modifications of the membrane lipid environment surrounding the enzyme.

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