Heterogeneity of Plasma High Density Lipoproteins*

Abstract

The homogeneity and stability of plasma alpha or high density lipoproteins (HDL, density 1.063 - 1.21) were studied by immuno- chemical techniques in combination with electrophoresis, ultracentrifuga- tion, and amino add analysis. These lipoproteins are demonstrated to undergo a transformation which may appreciably affect their quantita- tion under certain conditions. During prolonged storage, freeze-thaw- ing or centrifugation under both preparative and analytical conditions some of the native alpha lipoprotein, alpha LPA, is converted to a partially delipidated form, alpha LPb. These two forms have different electrophoretic mobility and density and are only partially cross reactive as antigens. These two forms have an important relationshp to the HDL subtractions conventionally measured in the ultracentrifuge. HDL, (D 1.063-1.1) consists solely of alpha LPA; HDL3 (D 1.1-1.21) contains both alpha LPA and alpha LFb; the latter was consistently demonstrated immunochemically in the fraction of D > 1.21, indicating that some alpha lipoprotein is present at a density greater than that usually attributed to lipoproteins.