PROTEINS. 87 



(g) Protamines. Simpler polypeptides than the proteins in- 

 cluded in the preceding groups. They are soluble in water, uncoag- 

 ulable by heat, have the property of precipitating aqueous solutions 

 of other proteins, possess strong basic properties and form stable 

 salts with strong mineral acids. They yield comparatively few 

 amino acids, among which the basic ones predominate. They are 

 the simplest natural proteins, e. g., salmine, sturine, clupeine, scorn- 

 brine. 



II. CONJUGATED PROTEINS. 



Substances which contain the protein molecule united to some 

 other molecule or molecules otherwise than as a salt. 



(a) Nucleoproteins. Compounds of one or more protein mole- 

 cules with nucleic acid, e. g., cy to globulin, nude ohist one. 



(b) Glycoproteins. Compounds of the protein molecule with a 

 substance or substances containing a carbohydrate group other than 

 a nucleic acid, e. g., mucins and mucoids (osseomucoid, tendomu- 

 coid, ichthulin, helicoprotein) . 



(c) Phosphoproteins. Compounds of the protein molecule with 

 some, as yet undefined, phosphorus-containing substances other 

 than a nucleic acid or lecithin, 1 e. g., caseinogen, vitellin. 



(d) Haemoglobins. Compounds of the protein molecule with 

 haematin, or some similar substance, e. g., haemoglobin, hcemocya- 

 nin. 



(e) Lecithopro tains. Compounds of the protein molecule with 

 lecithins, e. g., lecithans, phosphatides. 



III. DERIVED PROTEINS. 



i. PRIMARY PROTEIN DERIVATIVES. 



Derivatives of the protein molecule apparently formed through 

 hydrolytic changes which involve only slight alteration of the pro- 

 tein molecule. 



(a) Proteans. Insoluble products which apparently result from 

 the incipient action of water, very dilute acids or enzymes, e. g., 

 myosan, edestan. 



(b) Metaproteins. Products of the further action of acids and 

 alkalis whereby the molecule is so far altered as to form products 

 soluble in very weak acids and alkalis but insoluble in neutral fluids, 

 e. g. } acid metaprotein (acid albuminate), alkali metaprotein (alkali 

 albuminate) . 



1 The accumulated chemical evidence distinctly points to the propriety of classi- 

 fying the phosphoproteins as conjugated compounds, i. e., they are possibly 

 esters of some phosphoric acid or acids and protein. 



