FURTHER CHARACTERIZATION OF THE HUMAN SERUM D 1.063-1.21, Α1-Lipoprotein*

Abstract

The high density lipoprotein class floating at a solvent density between 1.063 and 1.21 g per ml can be fractionated by flotation in solvents of intermediate density into two major subfractions (1, 2), which according to Shore (3) have a protein moiety with identical amino acid composition and C-and N-terminal amino acids. Homogeneity of the D 1.063-1.21 lipoprotein in terms of protein moiety has also been indicated by immunochemical studies (4). It would appear, therefore, that the human serum high density lipoprotein of D 1.063-1.21 constitutes a group of molecules identical as to protein moiety and possibly differing only in lipid complement. The experiments reported below were designed to test this hypothesis. The serum D 1.063-1.21 lipoprotein was arbitrarily fractionated into three fractions floating respectively at solvent densities of D 1.063-1.125, 1.125-1.168, and 1.168-1.21. The results dealing with some of the physicochemical and biological properties of these lipoprotein subfractions form the object of this report. MATERIAL AND METHODSThe source of the lipoproteins was pooled sera from healthy human male subjects, fasted for at least 12 hours.

Plasma Lipoproteins in Liver Disease: I. Immunologically Distinct Low-Density Lipoproteins in Patients with Biliary Obstruction*

“…To ascertain a possible relationship of the apoprotein of the unreactive lipoprotein to those present in reactive lipoproteins, we performed amino acid analyses of lipoprotein fractions (Table III) (Table III, The results can be summarized as follows: the values for normal lipoproteins (Table III, columns 2-4) agree reasonably well with those reported by other workers (26)(27)(28)(29). The amino acids that are most helpful in distinguishing the three major lipoprotein classes (as discussed below) are aspartic, glutamic, isoleucine, and leucine.…”

Retinol-binding protein: the transport protein for vitamin A in human plasma

“…The amino acid composition of RBP differs from that of any previously reported plasma protein, including the protein moieties of both the high density, a-lipoprotein, and the low density, ,8-lipoprotein (27)(28)(29)(30)(31)(32)(33) of clefts in the three-dimensional structure of proteins, at their functional centers. Thus, myoglobin contains a cleft in its three-dimensional structure, and the heme prosthetic group resides within this cleft (35).…”

Heterogeneity of Plasma High Density Lipoproteins*

“…On the basis of the above experiments, the two forms of alpha lipoprotein distinguishable by immunoelectrophoresis have been designated as alpha LPA, the band of greater migration seen in plasma, HDL, HDL2, or HDL3; and alpha LPB, the second band present only in HDL3 and the density > 1.21 fraction ( Figure 7). This nomenclature incorporates the designation "LP" to differentiate the lipoprotein fromt the delipidated protein, alpha P. 3 Diffusion and precipitation studies. Small amounts of alpha LPB could be detected in fresh plasma by immunoelectrophoresis if the plasma was concentrated 5-to 10-fold by polyethylene glycol (15) Usually very small amounts of this second alpha band could be detected in unconcentrated plasma by Ouchterlony plates or especially by the method of Preer.…”

“…Subfractions isolated over different portions of the broad density band by which they are defined have been found to contain similar lipid composition and protein of the same amino acid composition (3). It is also usually accepted that the high density lipoproteins (HDL) are antigenically homogeneous (4,5) and form a single electrophoretic band.…”