Solution Properties of Apolipoproteins
We have learned from Dr. Lindgrens presentation that human serum lipoproteins are prepared customarily by preparative ultracentrifugation. Quantitation of individual density classes can than be performed with the analytical instrument. Thus we are so far only familiar with the operational classification of lipoproteins based on the method used for their separation, reflecting the hydrated densities. As it became evident from numerous publications of the past, and this has been clearly demonstrated at the Protides Meeting of this year, there exist a great variety of additional isolation and subfractionatioz procedures for serum lipoproteins. In fact we are able now to subfractionate lipoproteins not only according to their flotation behaviour in salt solutions of increased densities, but also according to differences in the protein moiety. Before going into the sometimes troublesome matter of purifying apolipoproteins it proved to be of great advantage to separate first lipoprotein subspecies or families. For that purpose it is necessary to apply not only one or two consecutive separation steps but rather a combination of some 3–6 different ones. After isolation of a maximum number of subfractions differing from each other by one or more apolipoprotein polypeptides they should be delipidated and further processed. This is particularly true since apolipoproteins once present in the lipid free state, tend to aggregate not only each apoprotein with the same species but also with all kinds of polypeptides from other families. Thus aggregates are folned with high molecular weights which in many cases cannot be dissociated quantitatively. Part of this presentation will therefore be devoted to the subfractionation of individual lipoprotein classes on a preparative scale followed by the description of the most effective and convenient delipidation procedures. Only the last part of this chapter deals with the solubility properties of individual apolipoprotein polypeptides — a matter which today is only poorly investigated. Before going into this field let us just summarize the present state of knowledge concerning the identity of apolipoprotein polypeptides of human serum.
KeywordsSolution Property Solubility Property Neuraminic Acid Hydrated Density Sodium Decyl Sulfate
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