THE DISTRIBUTION AND CHEMICAL COMPOSITION OF ULTRACENTRIFUGALLY SEPARATED LIPOPROTEINS IN HUMAN SERUM

In the past few years several methods have been developed for the analysis of serum lipoproteins.Lindgren, Elliott, and Gofman (1) have utilized the relatively low density of the lipoproteins to separate them from the other serum proteins by ultracentrifugal flotation.Quantitation was sub- sequently performed by refractometric methods in the analytical ultracentrifuge.Separations of lipoproteins have also been made by Cohn frac- tionation in cold ethanol, and the quantities of lipoprotein have been estimated from the lipid.content of the fractions (2, 3).Widely used at the present time is the method of zone electrophoresis with quantitation either by staining (4) or by chemical analysis of eluates from the support- ing medium (5, 6).Each of these methods has serious limitations.Analytical ultracentrifugal techniques (7, 8) require the possession of expensive equipment.The quantitation of data is subject to considerable error and gives no information regarding the chemi- cal composition of the lipoproteins.Cohn frac- tionation requires facilities for operation at -5°C.It permits accurate determination of the lipid com- ponents of the alpha and beta lipoproteins, but with this technique it is impossible to subfractionate these groups.With certain abnormal sera the method is unreliable (9).Determination of electrophoretically separated fractions by stain- ing techniques or by chemical analysis of eluates is subject to appreciable error.Both Cohn frac- tionation and electrophoretic techniques fail to separate lipoproteins from other serum pro- teins, thus making impossible the study of the protein moiety.The combination of preparative ultracentrifu- gation with chemical analysis of the separated fractions would seem to be a procedure by which both the distribution and composition of lipo- proteins could be determined simply and accu- rately.