COMPOUND PROTEINS. 167 



titatively into carbamino-acids. With the diamino-acid arginine, which 

 contains 4 nitrogen atoms, it is on the contrary only one-fourth because 

 this acid reacts with only one amino group, that of the a-amino valeric 

 acid chain. 



The reaction which has been developed and extensively used by 

 SIEGFRIED l and his pupils is of great value in the characterization of pep- 

 tones, kyrines, and proteoses, for the separation and fractional pre- 

 cipitation and for the determination of their constitution. The binding 

 of the carbon dioxide as carbamino-salts seems also in many ways 

 to be of physiological importance, as for example, the solubility of cal- 

 cium carbonate in alkaline fluids and for the carbon dioxide binding in 

 blood, etc. 



The amino-acids can by methylation form betaines, for example, 

 trimethy 1 gly cocoll or betaine CH 2 N (CHa) 3 . Betaine occurs abundantly 



I I 



CO -O 



in the plant kingdom. In the animal kingdom such bodies have been 

 found under physiological conditions in cold blooded animals and they 

 belong to those groups of bodies which have been called " aporrhegmas" 

 by ACKERMANN and KuTSCHER. 2 As " aporrhegmas " they designate 

 all those fractions of amino-acids from the protein, which can be pro- 

 duced from the proteins in a physiological manner and indeed in the life 

 of animals as well as the plants. These bodies are essentially the same 

 as have been observed in the putrefaction of the amino-acids and which 

 have been specially 'mentioned with every amino-acid described. 



The behavior of the amino-acids in yeast fermentation will be dis- 

 cussed in Chapter III. 



In regard to the methods for separating and preparing, in a pure form, 

 the various amino-acids and other products of protein hydrolysis which 

 have not been given in the preceding pages, we must refer to ABDERHAL- 

 DEN'S Handbuch der biochemischen Arbeitsmethoden, 1909-1910 Bd. 2. 



II. Compound Proteins. 3 



We designate as compound proteins those bodies which yield, on 

 cleavage, proteins (with their decomposition products) and other bodies 

 such as carbohydrates, nucleic acids, or pigments. 



The compound proteins known at present can be divided into three 

 groups: glycoproteins, nudeoproteins and chromoproteins. Of these the 



1 In regard to the literature see Siegfried in Ergebnisse d. Physiol. Bd. 9. 



2 Zeitschr. f. physiol. Chem., 69. See also Engeland, ibid., 69. 



3 Hoppe-Seyler has given the name proteide to these compound proteids, but as 

 this term is misleading in English we do not use it in English classifications in this 



