| Abstract: | The substrate properties of low-density lipoprotein (LDL) fractions from human and pig plasma and of lipoprotein a Lp(a)] upon incubation with either pig or human lecithin:cholesterol acyltransferase (LCAT, EC 2.3.1.43) were investigated and compared with those of pig high-density lipoproteins (HDL) or human HDL-3. The cholesterol esterification using purified native pig LDL-1, human LDL, or Lp(a) as a substrate was approximately 36-42% that of pig HDL or human HDL-3, while cholesteryl ester formation with pig LDL-2 was 41-47%. No significant difference was found in the substrate activity between pig HDL and human HDL-3, and between human LDL and Lp(a), respectively. After depletion of pig LDL-1, pig LDL-2, and human LDL from apolipoprotein A-I (apoA-I), cholesteryl ester formation decreased to about 22-28% of the value found with pig HDL. Depletion of human LDL from apolipoprotein E (apoE) did not result in significantly different esterification rates in comparison to native LDL. Total removal of non-apoB proteins from human LDL resulted in esterification rates of approximately 10-15% that of HDL. Readdition of apoA-I to all these LDL fractions produced solely in apoA-I-depleted LDL fractions an increase of cholesteryl ester formation, whereas in those LDL fractions that were additionally depleted from apoE and/or from apoC polypeptides, a further decrease in the esterification rate occurred.(ABSTRACT TRUNCATED AT 250 WORDS) |
