Studies on the interaction between gangliosides, protein and divalent cations

Abstract

In order to clarify the function of gangliosides in excitable membrane, the interaction between gangliosides, protein and divalent cations was studied both in a biphasic and in a single solvent system consisting of chloroform, methanol and water. The results are summarized as follows: 1. 1. Almost all of the added tri-, and disialogangliosides were recovered from the upper phase even in the presence of a large amount of CaCl 2. On the other hand, about 30% of the added monosialoganglioside was recovered from the lower phase under the same conditions. 2. 2. Ganglioside-bovine serum albumin-Ca 2 complex was formed at the interface in the biphasic solvent system. Maximal formation of the interfacial complex was observed, when 3 mg of bovine serum albumin and 10 μmoles of CaCl 2 were added to trisialoganglioside equivalent to 0.5 μmole of gangliosidic sialic acid. The complex forming ability of each ganglioside species with bovine serum albumin and CaCl 2 was in the following order: tri->di->monosialoganglioside. 3. 3. By the addition of methylated albumin (0.5 mg), as a model basic protein, about 80% of the added trisialoganglioside (0.52 μmole sialic acid) was incorporated into the interfacial complex in the biphasic solvent system. When added methylated albumin increased to more than 0.5 mg, the amount of interfacial complex decreased, and no trisialoganglioside was found at the interface following the addition of 2.0 mg of methylated albumin. 4. 4. The complex formation with ganglioside, bovine serum albumin and CaCl 2, or with ganglioside and methylated albumin was inhibited by the addition of KCl or acetylcholine. 5. 5. A hypothetical function of ganglioside-protein-Ca 2+ complex in synaptic membrane was proposed.