372 V. BLOOD LIPIDS 



total serum neutral fat is present in the zone of minimum density at the 

 top of the column, without appreciable amounts of protein. Cholesterol 

 was present in the fourth zone of high-medium density, but only in the form 

 of the ester; the highest concentrations of proteins (principally globulins) 

 were found in the densest zone (fifth zone), together with neutral fat and 

 phospholipids, but with no cholesterol. By the use of zone electrophoresis, 

 with a filter paper or starch medium containing barbital buffer, Kunkel 

 and Slater 155 were able to separate the a- and /3-lipoproteins into two main 

 fractions. The a-fraction had a lower free/total cholesterol ratio than did 

 the /3-component. The a-lipoprotein could be separated into either two 

 or three fractions, while the ^-lipoprotein consistently yielded at least three 

 fractions. In pathological sera with elevated lipid concentrations, the 

 a-lipoproteins were shown to diminish or entirely disappear concomitantly 

 with an increase in the /3-type. In some cases, a new component with an 

 abnormal mobility appeared in large amounts. 



According to Sandor et al., m euglobulins having a relatively alkaline 

 isoelectric point, and which represent 60 to 80% of these proteins, contain 

 only a small proportion of lipids. The amount of all lipids was found to be 

 higher in the euglobulins having an acid isoelectric point. Lipoproteins 

 were found during the precipitation of a- and /3-euglobulins. 



a. Types of Lipoprotein. The several plasma lipoproteins differ mark- 

 edly in their solubility in water and in ethanol-water mixtures, in their 

 molecular size and shape, in their electrostatic reactions, as well as in their 

 lipid content. The electrophoretic properties of the plasma lipoproteins 

 make it appear that one is an ai-serum globulin and the other a fr-serum 

 globulin. One of the most striking properties reported for the lipoproteins, 

 in contradistinction to the other plasma proteins, is their ready denatura- 

 tion when frozen or dried. In fact, the only satisfactory procedure for their 

 preparation in the native state is by the use of the Cohn procedure of plasma 

 fractionation, 153,157-159 which depends upon protein-protein interactions, 

 and in which fractional extraction has been largely replaced by fractional 

 precipitation. The great susceptibility of plasma lipoproteins to practi- 

 cally all types of denaturation explains why they were not prepared pre- 



156 H. G. Kunkel and R. J. Slater, J. Clin. Invest., 31, 677-684 (1952). 



156 G. Sandor, Y. Sabetay, and R. Vargues, Bull. soc. chim. biol., 35, 273-284 (1953). 



157 E. J. Cohn, J. A. Luetscher, Jr., J. L. Oncley, S. H. Armstrong, Jr., and B. D. 

 Davis, /. Am. Chem. Soc, 62, 3396-3400 (1940). 



168 E. J. Cohn, L. E. Strong, W. L. Hughes, Jr., D. J. Mulford, J. N. Ashworth, M. 

 Melin, and H. L. Taylor, J. Am. Chem. Soc, 68, 459-475 (1946). 



169 E. J. Cohn, J. L. Oncley, L. E. Strong, W. L. Hughes, Jr.. and S. H. Armstrong, 

 Jr., J. Clin. Invest., 23, 417-432 (1944). 



