Proteins of S_f 10-400 Lipoproteins from Lipemic Human Plasma^*

Abstract

The relationship of the St10-400 lipoproteins to chylomicrons and other low-density lipoproteins in human lipemic plasma was investigated by comparing the protein portion of the lipoproteins. The Sf 10-400 lipoprotein class was divided into five fractions, each with a different lipid composition and encompassing a different Sf range. N-Terminal amino acid analyses of these fractions showed little variation in their protein composition. Serine and threonine were the major Nterminals and aspartic and glutamic acids the minor N-terminals in all fractions. The same four amino acids also were found, but in different ratios, in the chylomicron and Sf 0-10 classes. The 5 f 10-400 lipoproteins from different plasmas were exhaustively extracted with T A he four major classes of lipoproteins in human plasma have different chemical and physical properties.Although each class is usually defined in terms of a specific range of densities or a corresponding range of flotation rates, the transition from the properties of one density class to those of another is gradual and continuous (Lindgren and Nichols, 1960;Searcy and Bergquist, 1962). Such a continuous spectrum of different lipoproteins suggests either that the classes are transformed from one into another in the plasma, or that the classes are unrelated but occupy overlapping density ranges. A knowledge of the extent to which these two possibilities occur is necessary for understanding the metabolic interrelationships, if any, that exist between the various lipoproteins.Characterization of the protein components of various lipoproteins is a useful method of identifying different lipoproteins. The evidence indicates that a small number of different proteins serves as structural elements for the

Solubilization and Properties of the Apoproteins of the Very Low- and Low-Density Lipoproteins of Human Serum*

“…Concerning LDL, (1.019 < p < 1.063), our Nterminal amino acid analyses are in agreement with the data by Shore (1957) and Rodbell (1957) but not with those of Bobbitt and Levy (1965). Further, ultracentrifugation of partially delipidated LDL showed two components, 10 and 15 S, whereas Avigan (1957) and Bobbitt and Levy (1965) reported a single fraction having s values of 13 and 15, respectively. Differences in the source of serum (normal vs. hyperlipemic), techniques of delipidation or solvent medium employed for the sedimentation analyses, may have accounted for the results.…”

“…Such conclusion, however, is not supported by the difference in solubility of these lipoproteins and by the results on their sedimentation and N-terminal amino acid analysis summarized in Table V, all pointing to the chemical dissimilarity between VLDL and LDL apoproteins. The peak maxima of one of the three sedimenting fractions obtained after partial delipidation of VLDL varied from author to author (Hayashi et al, 1959;Gustafson et al, 1964;Bobbitt and Levy. 1965).…”

Circulating Lipoproteins

“…The lipid composition of micellar lipoproteins has been presented elsewhere (14,23,(31)(32)(33)(34)(35)(36). Certain trends are of interest.…”