The Study of Serum Proteins and Lipids with the Aid of the Quantity Ultracentrifuge

We propose in the present paper to describe a system of lipoproteins which contain phospholipid but no free cholesterol and little or no esterified cholesterol. We utilize data which we have accumulated during the past four years during which time we have studied serum proteins and lipids by making multiple analyses of ten samples of each ultracentrifugate of untreated serum. The samples of centrifugate from standardized positions in the column are designated by numbers beginning with number one at the top, which is the cream layer sample.7 The detailed data have been published elsewhere,7'8 or are in process of publication. 4' 6 9 L0 The accumulated evidence from many sources, as reviewed by Edsall,2 indicates that serum lipids are in the main associated with proteins. Our data concerning the distribution of lipids and proteins in the ultracentrifugate provide both general and special support for that concept. Our finding, in low density centrifugate, of a concentration of globulin in excess of that expected from the albumin: globulin ratio of whole serum, along with high concentrations of lipids, strongly suggests that the globulin is there in increased concentration because of buoyancy provided by lipids attached in some fashion to the globulin molecule.7 Conversely, the finding of high concentrations of phospholipid and neutral fat in high density centrifugate indicates the attachment of these low density lipids in small proportions to many high density molecules. More specific information bearing upon this subject is provided by the systematic relationship between total globulin concentration and lipids at certain levels in the upper half of the column which we interpret as indicating stoichiometric relationships between proteins and lipids.8