Comparative studies on the low density lipoprotein subfractions from pig and man.

(1) By means of a single spin density gradient ultracentrifugation method, sera from six human volunteers and six pigs were studied; three or four distinct low density lipoprotein (LDL) subfractions could be seen in the pig serum (LDL-1A, LDL-1, LDL-2 and LDL-3) and three in the human serum (LDL-1A, LDL-1B and LDL-2). The subdivision of LDL into subfractions was less clear for the human subjects than for the pigs. (2) Physicochemical characteristics (chemical composition, apoprotein content, size and density) of the LDL subfractions were determined and showed many similarities. (3) In both species, in order of increasing density, relative protein content of the LDL subfractions increased, accompanied with a decrease in size. However total pig LDL was of higher density, smaller and contained more protein. (4) In conclusion, the pig appears a suitable animal model for the study of LDL heterogeneity. For these studies the density gradient ultracentrifugation method with visualization of the lipoprotein bands is the method of choice.