Sedimentation equilibrium of human low density lipoprotein subfractions.

The molecular weights of low density lipoprotein (LDL) subfractions were determined precisely by meniscus depletion sedimentation equilibrium. Equilibrium speeds ranged from 9743 to 5896 rpm. The average molecular weights of various LDL subfractions of Sf values 9.49, 7.94, 6.42, 5.17, and 3.71 determined by sedimentation equilibrium were 2.97 X 10(6) ; 3.13 X 10(6); 2.89 X 10(6); 2.45 X 10(6); and 2.61 X 10(6) daltons, respectively; and their respective densities were 1.0267, 1.0306, 1.0358, 1.0422, and 1.0492 g/ml. Minimal hydrated molecular weights for this fractions determined by flotation velocity at 37,020 rpm were 2.57 X 10(6); 2.37 X 10(6); 2.09 X 10(6); 1.94 X 10(6); and 1.81 X 10(6) daltons; whereas similar molecular weights determined at 52,640 rpm were 2.53 X 10(6); 2.27 X 10(6); 1.99 X 10(6); 1.86 X 10(6); and 1.74 X 10(6) daltons for the respective LDL subfractions. Higher molecular weights of fractions 2 and 5 compared to their adjacent fractions 1 and 4 by sedimentation equilibrium are of great interest. The calculated fractional ratio f/f O from sedimentation equilibrium and flotation velocity data ranges from 1.10 to 1.31, suggesting complexity and asymmetry of LDL subfraction molecules. There is also evidence that compressibility of LDL molecules may be different than that for the salt solution under high g-force. Assuming that redistributed LDL molecules at equilibrium under low g-force are spherical, it is possible that the shape of LDL molecules undergoing flotation velocity determinations may be distorted in high g-force conditions. Such distortion may be consistent with the high f/f O values obtained and may also be a basis for structural rearrangement and/or lipoprotein degradation with prolonged preparative ultracentrifugation at high g-force and pressure.