PROTEINS 169 



animal proteins as keratin (hair and feathers) and gelatin (hoofs 

 and horns). 



Conjugated Proteins.— The conjugated proteins yield a true 

 protein when hydrolyzed and, in addition, some other substance 

 of a quite different nature. They are rarely found in plants and 

 some groups are represented by only a few members. The chromo- 

 proteins are combinations of protein with a pigment. Hemoglobin 

 is such a protein, and the special pigments of the algae also belong 

 here (Chap. XV) . 



The mucilage from the root of the Japanese yam (Dioscorea) 

 is believed to be an example of glucoproteins, which are com- 

 pounds of protein with carbohydrates. The nucleoproteins are 

 compounds of nucleic acid with proteins and are the chief con- 

 stituents of the nuclei. They have been found by Osborne (1909) 

 in small amounts in the embryos of seeds, but whether these pro- 

 teins occur free there or are produced by the methods employed 

 in their isolation is uncertain. 



The phosphoproteins such as zymocasein in yeast are rarely 

 present in plants. They yield a protein and phosphoric acid, thus 

 bearing somewhat the same relation to the proteins that the 

 phospholipins do to the fats. The two substances are commonly 

 associated, e. g., in egg yolk, cheese, etc. Combinations of proteins 

 with phospholipins also exist and are known as lecithoproteins, 

 which are therefore a kind of phosphoprotein. 



Derived Proteins. — The derived proteins include decomposi- 

 tion products which are obtained from simple proteins by hydrol- 

 ysis or coagulation. They are transition products and do not 

 occur as permanent forms in the tissues. 



The metaproteins are the early products of hydrolysis by dilute 

 acids or alkalies. They are insoluble in water or salt solutions but 

 do dissolve in dilute acid and alkali. The coagulated proteins are 

 also primary derivatives which are produced by the coagulating 

 action of heat or alcohol. 



The proteoses or albumoses are produced from the simple pro- 

 teins by the action of hydrolytic agents such as the enzymes, 

 pepsin and trypsin. They are soluble in water, salt solutions, 

 dilute acids, and alkalies, but are not soluble in ammonium sul- 

 phate solutions. As found in almonds and wheat they give the 

 reactions for proteins but are not coagulated by heat. This is 

 the chief difference between the albumoses and the albumins. 



