Lipoproteins in human atherosclerotic vessels: II. Biochemical properties of the major apolipoproteins of arterial low density and very low density lipoproteins

Abstract

The biochemical behavior of the major apoproteins of low density lipoproteins (LDL) and very low density lipoproteins (VLDL) isolated from human atheroslerotic arteries was examined. On Sephadex G-150, delipidated arterial LDL behaved like delipidated serum LDL and eluted as a single peak (apoLDL) at the void volume. The apoLDL fractions migrated as a single band when examined by electrophoresis on cellulose acetate or acrylamide gel and had a mean sedimentation coefficient of 3.2. Upon double immunodiffusion arterial apoLDL formed immunopreciptin lines of complete identity with serum apoLDL, when reacted against antisera to either human serum apoLDL or LDL. However the amino acid composition of arterial and serum apoLDL was significantly different. When delipidated arterial VLDL was examined on Sephadex G-150, it separated into two major apoprotein fractions, SF-1 and SF-3, and into a minor SF-2 fraction. These fractions appeared to have similar elution volumes and immunochemical reactivity as the corresponding Sephadex fractions of delipidated serum VLDL. Arterial and serum SF-1, SF-2, and SF-3, when reacted respectively against apoLDL antisera, HDL antisera and apo C-III antisera, formed immunoprecipitin lines of complete identity. The sedimentation coefficients of arterial and serum SF-1 appeared similar, as were the coefficients of arterial and serum of SF-3. However the amino acid composition of arterial SF-1 and SF-3 was clearly distinguishable from that of their corresponding serum apoprotein fractions. When examined by acrylamide electrophoresis arterial and serum SF-3 showed a similar band pattern but with different electrophoretic mobility. SF-1 of arterial apoVLDL behaved much like apoLDL from arterial LDL as indicated by electrophoretic and immunochemical behavior and amino acid composition. Although the mean sedimentation coefficients of these apoprotein fractions were similar, the analytical pattern suggested SF-1 of arterial apoVLDL to be more polydisperse in its composition. The present studies indicate that major differences exist between the arterial and serum apoproteins especially in regard to their amino acid composition. They also suggest that arterial LDL and VLDL contain apoproteins which have some characteristics that are similar to the apoB and apoC proteins contained in serum LDL and VLDL.