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

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: (a) the binding process followed a biphasic kinetics with a break at 50 nM‐GM1; GM1 at concentrations below the break was stably associated, while over the break it was loosely associated; (b) stably bound GM1 activated (Na+, K+)‐ATPase up to a maximum of 43%; (c) the activation was dependent upon the amount of bound GM1 and was highest at the critical concentration of 20 pmol bound GM1× mg protein‐1; (d) loosely bound GM1 suppressed the activating effect on (Na+, K+)‐ATPase elicited by firmly bound GM1; (e) 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; (f) under identical binding conditions (2 h, 37°C, with 40 nM substance) all tested gangliosides (GM1, GD1a, GD1b, GT1b) activated (Na+, K+)‐ATPase (from 26–43%); NeuNAc, sodium dodecylsulphate, sulphatide and cerebroside had only a very slight effect. It is suggested that the ganglioside activation of (Na+ ‐K+)‐ATPase is 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.