FURTHER CHARACTERIZATION OF THE HUMAN SERUM D 1.063-1.21, α1-LIPOPROTEIN*

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Abstract
The human serum high-density lipoprotein (HDL) of solvent density between D 1.063 and 1.21 g/ml was fractionated by ultracentrifugation in solvents of intermediate density into 3 sub-classes D 1.063-1.125, D 1.125-1.168 and D 1.168-1.21. Their lipoprotein protein had identical absorption spectra and amino acid composition. When labeled with I131 and injected into mice, they showed the same half time of metabolic degradation (12 hours). These 3 HDL subfactions showed differences in flotation coefficient when analyzed at D 1.21 and had slight difference in electric mobility in starch gel. These differences appeared dependent on the lipid content of these fractions. Human serum HDL, labeled in the protein moiety with I131 and injected into human subjects and dogs disappeared from circulation according to a monomial exponential curve. When the dilipidated protein (Scanu et al. Arch. Biochem. et Biophys. 1958, 74, 390) was injected into either human subjects or dogs, it recombined with serum lipids and travelled with its own HDL class. It was postulated that serum HDL represent a single family of lipoproteins with identical protein component able to carry various amounts of lipids.