GLYOOPROTEINS. 163 



for every molecule C0 2 taken up. This quotient is equal to 1 for glycocoll 

 and the aliphatic aminq-acids because these go over quantitatively into 

 carbamino-acids. With the diamino-acid arginine, which contains 4 nitro- 

 gen 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. 



This behavior, which has been further studied by SIEGFRIED with 

 NEUMANN and LIEBERMANN, is valuable in determining whether we are 

 dealing with a mixture of protein cleavage products or a combination of 

 these, as the quotient becomes larger by the splitting of a peptide bind- 

 ing. As the quotient also increases during the progress of digestion 

 SIEGFRIED and his collabprators have attempted to control the progress 

 of proteolytic cleavage by determining this quotient. 



II. Compound Proteins 1 



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, nucleoproteins and chromoproteins. Of these the 

 last-mentioned group (haemoglobin and hsemocyanine) will be discussed 

 in a subsequent chapter (Chapter VI on the blood) . 



a. Glycoproteins (glucoproteins). 



Glycoproteins 2 are those compound proteins which on decomposition 

 yield a protein on the one side, and a carbohydrate or derivatives of 

 this on the other, but no purine bodies. Some glycoproteids are free 

 from phosphorus (mucin substances, chondroproteins, and hyalogens), 

 and some contain phosphorus (phosphoglycoproteins) . 



The glycoproteins free from phosphorus may, as regards the nature 

 of the carbohydrate groups split off, be divided into two chief groups, 

 the mucin substances and the chondroproteins. The first yield on hydrolytic 



1 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 

 sense. 



2 Abderhalden (Lehrb. d. physiol. Chem., 1909, p. 191) has proposed dropping the 

 name glycoproteids entirely and to consider these bodies as simple proteins, because 

 it has not been shown that the carbohydrate groups occupy the same relationship 

 to the protein component that the hsemin or the nucleic acid bears to the haemo- 

 globin or the nucleoprotein molecule. It is possible that this proposition, which is 

 not applicable to the entire group (including the proteins containing chondroitin- 

 sulphuric acid) but applies only to the mucin group, will be found in the future to be 

 correct. It is the opinion of HAMMARSTEN that it is better to wait for further research 

 in this direction before we drop the generally accepted nomenclature and the usual 

 subdivisions of the proteins. 



