出版社：American Society for Biochemistry and Molecular Biology
摘要：Human serum low density lipoprotein of d 1.019-1.063 (LDL2) treated with succinic anhydride at pH 7.5-8.0 showed the same chemical composition, hydrodynamic properties (flotation and sedimentation coefficients, intrinsic viscosity) and optical properties (circular dichroism) as untreated LDL2. However, in contrast to LDL2, the succinylated product (s-LDL2) failed to react with rabbit anti-LDL2 antisera. Extraction with ethanol-ether 3:1 yielded the succinylated apoprotein (s-apo-LDL2), which was, unlike untreated apoprotein, soluble in aqueous buffers. Succinylated apoprotein, which was also immunologically unreactive, appeared to differ in structure from s-LDL2, as assessed by the parameters of intrinsic viscosity and circular dichroism. The molecular weights of both LDL2 and s-LDL2 obtained by the technique of sedimentation equilibrium were 2.1-2.3 × 106. By the same method, s-apo-LDL2 gave an uncorrected figure of 3.95-4.15 × 104 and, after correction for succinyl functions, of 3.60-3.80 × 104. Because of the assumptions made in the computations, the latter figure was considered approximate. The marked differences in molecular weight between s-apo-LDL2 and whole apo-LDL2 (̃5 × 105) were taken to support the subunit structure of apo-LDL2, which is envisaged as an aggregate of about 12 subunits which dissociate upon succinylation. Further, the large percentage (about 90%) of the free amino groups of LDL2 found to react with succinic anhydride suggests that these groups are at the surface of the molecule.
