84 THE ACTION OF ENZYMES 



phosphorus, and are acid substances, capable of forming 

 definite salts with alkalis. The pure phospho-proteins 

 are insoluble in water, and are thrown down when acids 

 are added to solutions of their salts. 



(7) Conjugated proteins. For these bodies German 

 writers adopt the generic term " proteid." They are 

 compounds which contain a protein united with a radical 

 or molecular group, termed a " prosthetic group." The 

 latter is either (i) a nucleic acid, (2) a carbohydrate, or 

 (3) a coloured product. As the peculiar characters of 

 the conjugated proteins are chiefly dependent upon the 

 kind of prosthetic group which they contain, they may 

 be conveniently divided into three sub-classes, viz. : (a) 

 Nucleoproteins, (b) Glucoproteins, and (c) Chromoproteins. 

 On hydrolysis by acids or enzymes a conjugated protein 

 splits into its prosthetic group and a protamine, histone, 

 or other protein. 



(8) Derivatives of proteins. When proteins are acted 

 upon by weak acids or enzymes they undergo hydro- 

 lysis, some of the products of decomposition being sub- 

 stances which give the reaction of proteins, but are 

 simpler in construction than the original body from 

 which they have been obtained. The chief of these 

 derived proteins are : 



(a) M eta-proteins, the so-called acid-albumins and alkali- 

 albuminates, formed by the gentle action of dilute acids 

 and alkalis respectively on proteins, belong to this class. 



(b) Proteoses.- A group which embraces albumoses, 

 globuloses, gelatoses, etc. These substances are simpler 

 transformation products of proteins than the meta-pro- 

 teins. They can be salted out of acid solutions by 

 ammonium or zinc sulphate, but are not coagulated by heat. 



(c) Peptones. Further hydrolysis of the proteoses 



