title: Physiocochemical properties of low-density lipoproteins of normal human plasma. Evidence for the occurrence of lipoprotein B in associated and free forms.
abstract: 1. Low-density (d 1.006-1.063g/ml) lipoproteins from normal human plasma were separated by differential preparative ultracentrifugation into six subfractions. Each low-density (LD) lipoprotein subfraction contained lipoprotein B as the major and lipoproteins A and C as the minor lipoprotein families. 2. Three lipoprotein B subfractions (LP-B), LP-B-III (d 1.019-1.030g/ml), LP-B-IV (d 1.030-1.040g/ml) and LP-B-V (d 1.040-1.053g/ml) were prepared from the corresponding LD lipoprotein subfractions by immunoprecipitating small amounts of lipoproteins A and C. 3. Determination of hydrodynamic properties indicated that LD lipoproteins consisted of three molecular segments characterized by a stepwise change in the molecular weight: LDL-I and LDL-II subfractions (d 1.006-1.019g/ml) with an average mol.wt. of 4.75x10(6), LDL-III (d 1.019-1.030g/ml) with a mol.wt. of 3.99x10(6), and LDL-IV, LDL-V and LDL-VI (d 1.030-1.063g/ml) with a mol.wt. of 2.85x10(6). 4. All three lipoprotein B subfractions had an average mol.wt. of 3.16x10(6). 5. The LDL-I and LDL-II subfractions consisted of lipoprotein B and lipoprotein C families which were present in the form of an association complex. This was isolated from serum by immunoprecipitation with antibodies to lipoprotein B. The complex had a mol.wt. of 4.35x10(6). 6. The results indicate a fundamental difference between the LD lipoprotein subfractions with d 1.006-1.019g/ml and those subfractions with d 1.030-1.063g/ml. In the former, lipoprotein B occurs as a part of an association complex, whereas in the latter it occurs as a separate entity.
mesh_terms: D000818:Animals; D004058:Diffusion; D005215:Fasting; D005260:Female; D006041:Goats / Q000276:immunology; D006801:Humans; D005779:Immunodiffusion; D008077:Lipoproteins, LDL / Q000097:blood* / Q000302:isolation & purification; D046911:Macromolecular Substances; D008297:Male; D008433:Mathematics; D008970:Molecular Weight; D011487:Protein Conformation; D011817:Rabbits / Q000276:immunology; D013997:Time Factors; D014461:Ultracentrifugation; D014783:Viscosity
chemical_list: D008077:Lipoproteins, LDL; D046911:Macromolecular Substances