METAPROTEINS 95 



of the nucleoproteins, they do not yield any purine or pyrimidine bases on 

 hydrolytic cleavage. Two of the best known phosphoproteins are the 

 casein of milk, and vitellin of the egg yolk. The phosphorus is apparently 

 present as a phosphoric acid ester. 



Hemoglobins. These are compounds of the simple protein histone, 

 with an iron-, or in some lower animals, copper-, or manganese-containing 

 pigment substance. The hemoglobins are more fully discussed in the chapter 

 on the Blood. 



Lecithoproteins. These are combinations of proteins and a fat-like 

 substance, lecithin. Lecithin is a compound of fatty acids, glycerin, phos- 

 phoric acid, and an ammonium-like organic base, choline. The combination 

 of lecithin and protein is apparently a loose one: the lecithin ordinarily can 

 be split off by boiling alcohol. The lecithoproteins include substances 

 commonly termed lecithans and phosphatids. 



The derived proteins are formed as intermediate products in the hydro- 

 lytic cleavage of the original protein molecule. The primary protein de- 

 rivatives are "apparently formed through hydrolytic changes which involve 

 only slight alteration of the protein molecule." 



Metaproteins. These are formed from the simple proteins by the 

 action of weak acids and alkalies. This class comprises what have com- 

 monly been termed acid and alkali albuminates. The metaproteins are 

 soluble in acid or alkaline solution, but are insoluble in neutral solutions. In 

 the formation of alkali metaproteins, the sulphur in organic combination 

 is split off. Thus the alkali metaprotein differs from the acid metaprotein 

 in that the former contains little or no sulphur. It is impossible, then, to 

 transform an alkali metaprotein into an acid metaprotein, though the acid 

 metaprotein can be changed into the other modification. Acid metaproteins 

 are the first products formed in the pepsin hydrochloric acid digestion of 

 proteins. 



Coagulated Proteins. Unaltered typical simple proteins in solution are 

 altered when heated or by long standing under alcohol. They are transformed 

 into a coagulated modification no longer soluble in water or dilute salt solu- 

 tions. A similar change occurs when solutions of the proteins are con- 

 tinuously shaken or by the action of enzymes, as in the formation of fibrin 

 from fibrinogen in the clotting of the blood. On treating coagulated proteins 

 with acids or alkalies they are converted into the respective metaproteins. 



Secondary Protein Derivatives. Secondary protein derivatives are 

 intermediary cleavage products which result from a more profound change 

 than occurs in the formation of the primary derived protein. 



Proteases or albumoses are intermediate products in the digestion of 

 proteins by proteolytic enzymes or in the cleavage with acids. Peptones 

 are yet more simple products than the proteoses and are to be regarded 

 as relatively simple polypeptides which still retain some of the protein 



