Structure of two subfractions of normal porcine (Sus domesticus) serum low-density lipoproteins. X-ray small-angle scattering studies.

Two subfractions of low-density lipoproteins (LDL) were isolated from normal pig (Sus domesticus) serum by a combined method including precipitation, ultracentrifugation, and gel chromatography. The fractions recovered from the buoyant density ranges 1.020-1.050 and 1.050-1.090 g/mL, denoted as LDL1 and LDL2, respectively, were studied with regard to structure and thermotropic behavior by X-ray small-angle scattering and were compared to human serum low-density lipoprotein of density 1.020-1.063 g/mL. The average molecular weights determined from the scattering intensities on absolute scale were 2.6 X 10(6) and 2.0 X 10(6) for LDL1 and LDL2, respectively. The maximum particle diameters were found to be 24 and 21 nm, respectively. Both species were found to have quasi-spherical symmetry and to display the thermotropic transition of the apolar lipids within the particle core similar to human LDL. The width of the transition was approximately 9 degrees C in both cases, but the midpoint transition temperature was higher by 8 degrees C for LDL1 (33 degrees C) than for LDL2 (25 degrees C). Despite their different sizes and thermotropic behavior, the two porcine LDL subfractions appear to be built according to the same structural principle as human LDL in the molecular organization of the apolar lipids within the particle core.