title: Human plasma lipoprotein [a]. Structural properties.
abstract: When lipoprotein [a] was isolated in the presence of the proteolytic inhibitor Trasylol, its apoprotein exhibited one dominant band corresponding to a molecular weight of about 1.2 million when analyzed by electrophoresis on 3.25% sodium dodecyl sulfate-polyacrylamide gels. After chemical reduction, this band was missing but was replaced by two bands, one corresponding to a molecular weight of about 490,000 and the other to a molecular weight of about 645,000. Before treatment with reducing agents, the apolipoprotein [a] and apolipoprotein B immunoreactivities were detectable in the same electrophoretic band, but after reduction the apolipoprotein [a] was demonstrated to be separate from the apolipoprotein B. These results suggest that the apoprotein of lipoprotein [a] is composed of two subunits which are similar in molecular weight and are held together by one or more disulfide bonds. One subunit possesses apolipoprotein [a] and the other apolipoprotein B immunoreactivity. The secondary structure of the apoprotein components within lipoprotein [a] has been studied by circular dichroism and found to differ significantly from the secondary structure of the apoproteins in low density lipoproteins and high density lipoproteins. About 30% alpha-helical structure was measured in lipoprotein [a] compared to 48% in low density lipoproteins and 70% in high density lipoproteins. Lipoprotein [a] exhibited a much higher percentage of disordered structure than either of the other two lipoproteins.
mesh_terms: D002942:Circular Dichroism; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007123:Immunoelectrophoresis, Two-Dimensional; D017270:Lipoprotein(a); D008074:Lipoproteins / Q000097:blood*; D008075:Lipoproteins, HDL / Q000097:blood; D008077:Lipoproteins, LDL / Q000097:blood; D008970:Molecular Weight; D011487:Protein Conformation
chemical_list: D017270:Lipoprotein(a); D008074:Lipoproteins; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL