Amino acid composition of the proteins from chylomicrons and human serum lipoproteins.

By a combination of polyanion precipitation and ultracentrifugation, chylomicrons, very low density, low density, and high density lipoproteins have been isolated from human serum as discrete classes free from contamination with any other major class of lipoprotein or protein. After removal of the lipid, the proteins from each class were hydrolyzed and their amino acid compositions were determined by use of the amino acid analyzer. Application of the "t" test to the concentrations of amino acid residues showed that the amino acid composition of the proteins from each of these lipoprotein classes differs significantly from class to class. However, when the logarithms of the moles of amino acid residues are plotted, there are similarities in the amino acid "profiles" between the chylomicrons and high density lipoproteins on the one hand, and between the very low density and low density lipoproteins on the other. The differences in amino acid composition between the lipoproteins suggest that any metabolic interconversions between them probably do not occur by simple lipolysis.