222 



Solubility o£ Proteins 



Chick,"^ S0rensen," and others have studied the phosphorus content of serum 

 proteins as a measure of the phosphoHpids present. The phospholipid is 

 largely combined with the water-insoluble proteins. The phosphorus content 

 may be higher than 0.3 per cent, which corresponds to 7.5 per cent of phospho- 

 lipid. MacheboeuP has described a protein containing a much higher percent- 

 age of phospholipid as well as cholesterol. Cholesterol has also been reported in 

 both the euglobulin and albumin fractions."' ^■^'' KendalP reports the pres- 

 ence of a fatty acid associated with crystalline human albumin "that cannot be 

 removed without first destroying the albumin" (p. 109). 



TABLE 1 

 Galactose-Mannose Content of Horse Serum Globulins 



Rimington^" (i9,'!i) 



S(zirensen and Haugaard^' (1933) 

 Tiselius'* (i937) 



Hewitt23 (1938) 



Per cent of 

 carbohydrate 



2.0 



1.8 



0.7 

 2. 2 

 0.4 



1-4 



2.4 

 5.6 



Fraction analyzed 



Total globulins 



Total globulins 



Gamma globulin 

 Beta globulin 

 Alpha globulin 



Pseudoglobulin A 

 Main pseudoglobulin 

 Globoglycoid 



The carbohydrate bound to serum proteins is reported to be probably 

 galactose-mannose-acetylglucosamine.'^'^" The only protein free from bound 

 carbohydrate is one of the crystalline albumins; the other crystalline albumin 

 contains about 5 per cent of carbohydrate; and Rimington^^ describes the 

 noncoagulable protein from serum, seromucoid, as containing 10.7 per cent 

 of carbohydrate. Various authors have investigated the carbohydrate content 

 of globulins and their results on horse serum are given in table 1. 



The most extensive survey of the carbohydrate content of serum proteins 

 has been carried out by Hewitt,^' ^^ who divides the globulins from the serum 

 of a number of species into his two euglobulin fractions and at least three 

 pseudoglobulins, the most insoluble. A, the main fraction, and globoglycoid 

 which contains up to 5 per cent of carbohydrate. We^^ have obtained similar 

 results with a more extensive fractionation. The pseudoglobulin may be di- 

 vided into more fractions and, as Hewitt suggests, it is possible to obtain 

 pseudoglobulin with a somewhat lower carbohydrate content. However, none 

 have been found to be carbohydrate free. 



It is evident that proteins really combine with these smaller organic mole- 

 cules as Hewitt^ says: "That the polysaccharide present in protein forms an 

 integral part of the protein molecule and is not merely a loosely bound con- 



