Lipoproteins sedimentation coefficient

Svedberg flotation rate (analogous to a negative sedimentation coefficient) is the rate at which each lipoprotein floats up through a solution of sodium chloride of specific gravity 1.063. 

The lipoprotein density that should be employed in Eq. (2) is the buoyant density, which is the density at which the sedimentation coefficient is equal to zero. The buoyant density was obtained experimentally by measuring the sedimentation coefficient at several solvent densities and extrapolating to zero. Kahlon et al. (1982) have shown that the buoyant densities, which they call the a densities, vary with the rotor speed of the centrifuge, reflecting the different compressibilities of water and lipid. In order to convert the lipoprotein density, as determined from its composition, to the buoyant density at a rotor speed of 52,640, the data of Kahlon et al. (1982) were used calculate a correction factor of 0.0016 g/ml, which was added to the compositional densities. The values of buoyant densities listed in Table 11 have been calculated by adding 0.0016 g/ml to the density values determined from their compositions. 

Utilizing the buoyant densities listed in Table II and the frictional ratio of 1.11, values for the sedimentation coefficient have been calculated at two different solvent densities the standard S value routinely used to characterize human serum lipoproteins is defined as value of the flotation coefficient in Svedberg units (the negative sedimentation coefficient X 10 sec) in an aqueous NaCl solvent with a density of 1.063 g/ml and a viscosity of 1.021 centipoise (the viscosity of a 1.063 g/ml sodium chloride solution at 26°C). These values are listed in Table II. The S value is very sensitive to small variations in lipoprotein density because the solvent density is close to the lipoprotein density. To compare the particle sizes or molecular weights, values of the sedimentation coefficient (5) in a solvent with a density of 1.20 g/ml and the viscosity of KBr at 25°C are preferred, and the computed values are listed in Table II. 

Table 5. Molecular weights and sedimentation coefficients for lipoproteins from ovaries and hemolymph of crustaceans... 

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