IDENTIFICATION AND QUANTIFICATION OF APOLIPOPROTEINS IN ADDITION TO APO[A] AND APO B-100 IN HUMAN LIPOPROTEIN[A]

The protein moiety of Lp[a] is widely believed to consist of one molecule of apo B-100 and one molecule of apo[a] per particle, linked by at least one disulfide bond. In this study we have re-examined the composition of Lp[a] to determine if other less abundant apolipoproteins might be present. Analysis of Lp[a] by sodium dodecyl sulfate-polyacrylamide electrophoresis under reducing conditions showed bands corresponding to <200 kD but >50 kD, 40 kD, 26 kD, 23 kD and 9 kD when stained with silver. Western immunoblot analysis of three preparations of Lp[a] revealed the presence of apoE and apoD. Enzyme-linked immunoassays were used to quantify apoA-I, apoA-II, apoC-I, apoC-II, apoC-III, apoE and apo B-100 in Lp[a] and autologous LDL isolated from three healthy males. There isa significant amount of apoA-I in the Lp[al, although the levels varied widely among the different samples. ApoE concentrations were consistent in the three Lp[a] samples and were beween 22 and 26% of relative apo B-100 concentrations. Relatively minor amounts of apoA-II and no apoCs were detectable in the three Lp[al preparations. In contrast, the autologous LDL preparations contained relatively higher amounts of apoA-I, apoA-II, apoE, apoC-I, apoC-II and apoC-III. The identity of the multiple bands corresponding to <200 kD and >54 kD and 9 kD is not established.