Interaction of GM1 Ganglioside with Bovine Serum Albumin Formation and Isolation of Multiple Complexes

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Abstract
The binding of ganglioside GM1 to bovine Serum albumin has been studied by using absorption and fluorescence properties of the protein chromophores. Differences to the ultraviolet absorption spectrum and in fluorescence quenching, as well as a marked shift of the wavelength at the fluorescences maximum provide information about the binding of this ganglioside to albumin. Ultracentrifugal studies showed that there are two forms of the GM1‐protein complexes which differ markedly in their molecular weight. These two forms have been separated on this basis, by a chromatographic sieving procedure, and designated as complexes I and II. Both complexes are characterized by it GM1: protein ratio of one ganglioside micelle per albumin polypeptide chain. Complex II polymerizes slowly and irreversibly to a dimer, complex I. These results have been correlated with the optical studies in order to draw limited inferences its to the environment of the binding sites on the native protein. The interaction between GM1 micelles and albumin is mostly hydrophobic and the two complexes are actually mixed ganglioside‐protein micelles. At submicellar concentrations of ganglioside a binding of ganglioside GM1 to albumin also occurs. This process is due, however, to an aspecific, reversible adhesion of GM1 molceules on the albumin surface with no apparent perturbation of the albumin structure.