The Α2 LIPOPROTEINS OF HUMAN SERUM. CORRELATION OF ULTRACENTRIFUGAL AND ELECTROPHORETIC PROPERTIES

Abstract

Two main groups of lipoproteins have been characterized in the serum of normal adults.These have been termed the a1 and the 8,/ lipoproteins on the basis of their electrophoretic mobility (1-5). The broad spectrum of low density lipoproteins that have been observed particularly in patients with arteriosclerosis by means of the analytical ultracentrifuge (6) have not been classified in terms of electrophoretic mobility because of the difficulties in characterization by classical electrophoretic procedures (7-9). Nevertheless, these lipoproteins have usually been considered as /3 lipoproteins.Electrophoresis on filter paper, obviating solution density problems and permitting lipid analyses of the more stable whole serum has revealed the two main "alpha" and "beta" lipoprotein components. Another fraction observed at the site of origin is considered to represent adsorbed lipoproteins (4, 5) particularly the chylomicrons (10).This fraction is not observed by zone electrophoresis in a starch supporting medium, but an additional lipoprotein peak in the a2 region has been found in the sera of fasting normal (4, 11) and arteriosclerotic (12) individuals. Relatively little information is available regarding this component except that it was shown to rise after meals, particularly fatty meals, as indicated by phospholipid determinations (11).The present report represents an attempt to define the a2 lipoproteins further in terms of both zone electrophoretic and density ultracentrifugalproperties. This fraction was examined in the sera of a limited group of fasting normal and arteriosclerotic individuals and was found to consist primarily of lipoproteins less dense than d2"1.018. METHODSPreparative ultracentrifugation of the human sera was carried out in accordance with the basic principles of differential density centrifugation of the lipoproteins as described by Lindgren, Elliott, and Gofman (13) and de Lalla and Gofman (14) with very minor modifications. The Spinco swinging bucket rotor SW39L was used in the Spinco Model E ultracentrifuge instead of the angle preparative rotors. Various low molecular weight solutes were used to effect density increments for isolation of low density fractions and initially layered solutions were routinely employed.The purposes of this study were met by a gross fractionation with no density gradient of solvent but rather one due to the distribution of the serum albumin after the centrifugation to effect sufficient compartmentization to quantitatively maintain the separation of the serum into top and bottom fractions. Very slow acceleration and deceleration were employed, approximately 1000 rpm per min. In the Model LH preparative machine the insertion of a drive current meter enabled acceleration and braking at a given constant current similar to the operation of the Model E. This required constant manual slow movement of the speed dial. In general the Model L machine proved less satisfactory for accurate work with the swinging bucket rotor because of disturbance just prior to stopping.In ...

The nature of pre beta (very low density) lipoproteins.

“…The correlations between lipoprotein bands and fractions obtained in normal subjects by different methods are shown in Figure 1. All have been substantiated experimentally (3,4,7).…”

The Lipid Composition of Serum in Patients With Liver Disease*

“…It has been suggested that the hyperlipemia of obstructive jaundice is a consequence of the retention of cholate in the plasma with a resultant trapping of plasma lipids (44)(45)(46). This explanation seems unlikely, however, because the amount of bile salt in the serum of patients with jaundice is much smaller than the amounts of leci-2 The fractions D < 1.063 and > 1.063 migrate as #-and a-globulin, respectively, on paper electrophoresis (19), while the fraction D < 1.019 migrates as a.2 globulin on zone electrophoresis (43). thin and free cholesterol (47,48) and apparently most of the bile salt is bound to albumin (49).…”

Pre-beta-very low density lipoproteins as precursors of beta-very low density lipoproteins. A model for the pathogenesis of familial dysbetalipoproteinemia (type III hyperlipoproteinemia).

“…Lipoproteins were separated by electrophoresis using a Pevikon block (Mercer Consolidated Corp., Yonkers, NY) (38,39). Human LDL were used as a reference for f,-electrophoretic mobility for each Pevikon block.…”