ABSTRACT
Aggregation properties of gangliosides, the major synaptic membrane glycosphingolipids of mammalian brain, may prevent their segregation during membrane assembly and promote a uniform membrane matrix with minimum maintenance energy. The sphingosine residues of bovine brain gangliosides show an increase in C20-sphingosine corresponding with an increase in sialic acid. Concentrations of C20-sphingosine varied from 37% for the monosialoganglioside to 64% for the trisialoganglioside, the remainder being C18-sphingosine. Ultracentrifugal analysis showed that changes in sialic acid content and in C20-sphingosine content individually affect micellar size. Increases in sialic acid content decreased micellar size from 225 for the monosialoganglioside to 120 monomersper micelle for the trisialoganglioside. Monosialogangliosides enzymatically prepared from oligosialohomologues with a higher C20-sphingosine content gave evidence for a considerable effect of C20sphingosine upon the free energy of the aggregate form; the number of monomers per micelle increased from 225 for the natural monosialoganglioside to 280 for monosialoganglioside derived from trisialoganglioside. The similar aggregation energies of the major synaptic membrane gangliosides apparently result from a metabolic balancing of increased C20-sphingosine with increased sialic acid content.
Subject(s)
Gangliosides , Sphingosine , Animals , Binding Sites , Brain Chemistry , Cattle , Chromatography, Gas , Micelles , Molecular Weight , Oligosaccharides/analysis , Structure-Activity RelationshipABSTRACT
The use of a single high-speed sedimentation equilibrium experiment to analyze mixed associating systems is inadequate to determine the association mode even if the molecular weight of one species is known. Simultaneous analysis of the concentration distributions at three equilibrium speeds greatly reduces the lack of uniqueness. Linear least-squares multi-speed fits discriminate between association models in which the molecular weights are assumed. Experiments at a series of initial concentrations as well as rotor speeds further increases the discrimination. An overspeed procedure is proposed. The overspeed time depends only slightly on the sedimenting species molecular weight, but significantly on the frictional ratio. A minimal overspeed time may be estimated.
Subject(s)
Ultracentrifugation/methods , Binding Sites , Kinetics , Macromolecular Substances , Mathematics , Molecular WeightABSTRACT
Histone interactions in solution may depend upon treatments used for purification. Optical rotatory dispersion and sedimentation-velocity measurements have been made in a reference solvent, before and after exposure to various treatments, to investigate histone susceptibility to irreversible denaturation. Some acid conditions and urea and guanidine solutions may denature. Interaction studies performed on nondenatured histones indicate that the dimer, (H4)(H3), and tetramer, (H4)2(H3)2, dissociate to monomers at low ionic strength. Sedimentation-velocity experiments suggest a model for the (H4)2(H3)2 tetramer, with a compact semispherical center and four protruding amino-terminal regions. Fractions H2a and H2b interact to form the mixed dimer in equilibrium with monomers. Fraction H2a self-associates readily to dimers, tetramers, and octamers, while fraction H1 associates only weakly to form dimers.
