BLOOD 



nism. Indeed they are so effective that the characteristic 

 properties of the Hpids are completely submerged and are 

 dominated by the hydrophilic properties of the proteins. Al- 

 though the first lipoprotein was isolated from horse plasma by 

 Macheboeuf in 1929 (22), little attention was paid this highly 

 important class of conjugated proteins until World War II. 

 Since then they have received the intense scrutiny of both 

 chemists and clinicians. The chemical focus has been directed 

 primarily toward the isolation and study of the composition and 

 structure of the lipoproteins. Because of the disparate nature of 

 the chemical moieties involved, the lipoproteins have an inherent 

 fragility; the most extreme example is probably the /3-lipo- 

 protein which has been extensively studied by Oncley and 

 collaborators (26). The composition of this species is pre- 

 dominantly lipid ; only 23% of the anhydrous weight is peptide. 

 Despite this, the substance has characteristic protein-like solu- 

 bility properties. The lipid constituents show a striking lack of 

 solubility even when the molecule is exposed to organic solvents. 

 Only after the lipoprotein has been denatured do the lipids pass 

 freely into the organic layer. The forces which hold the molecule 

 together appear to be largely of the van der Waals type. Oncley 

 has calculated that even if spread in a layer one peptide chain 

 thick, on the surface of the spherical molecule, the peptide moiety 

 would cover only about half the surface. If the charged polar 

 groups of the phospholipids were also oriented at the surface, 

 these would contribute further to the amphoteric behavior of the 

 molecule. Such an arrangement at the surface would result in 

 an interior structure composed chiefly of water and nonpolar 

 lipids. The structural importance of the water is suggested by 

 the deep-seated, irreversible, changes which occur when the 

 state of the water is changed, as by freezing or drying. 



Clinical interest in the plasma lipoproteins derives from the 

 finding that they may reflect predisposition toward or actual 

 occurrence of certain diseases such as atherosclerosis, of which the 

 characteristic lesion is a fatty deposition in certain areas of the 

 circulatory system. Barr and collaborators in New York (4), 



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