Immunological properties of bovine serum lipoproteins and chemical analysis of their protein moieties.

Four classes of bovine serum lipoproteins were isolated by precipitation with dextran sulfate, ultracentrifugation, and preparative electrophoresis on polyacrylamide gel. Very low density lipoprotein (d less than 1.019 g/ml) was related immunologically to low density lipoprotein-two (d 1.039 to 1.060 g/ml) and high density lipoprotein (d 1.060 to 1.210 g/ml) was related immunologically to low density lipoprotein-one (d 1.019 to 1.039 g/ml), but the two pairs were immunologically distinct. The major N-terminal amino acid of both high density lipoprotein and low density lipoprotein-one was aspartic acid, and that of low density lipoprotein-two was glutamic acid. Very low density lipoprotein had both aspartic acid and glutamic acid as the major N-terminal amino acids. None of the lipoproteins was identical with any other with respect to amino acid composition, but high density lipoprotein and low density lipoprotein-one were similar to each other and different from low density lipoprotein-two. Very low density lipoprotein was similar to both low density lipoprotein-one and low density lipoprotein-two. It is concluded that the proteins of high density lipoprotein and of low density lipoprotein-one are related and are different from that of low density lipoprotein-two. The protein of very low density lipoprotein is related to that of low density lipoprotein-two but may contain polypeptides of high density lipoprotein or low density lipoprotein-one.