168 THE PKOTEIN SUBSTANCES. 



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

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



A. Glycoproteins (glucoproteins). 



Glycoproteins l are those compound proteins which on decomposi- 

 tion 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 

 cleavage an amino-sugar, which has been shown to be glucosamine in 

 all but a few exceptions. 2 In the chondroproteins, on the contrary, the 

 protein is united to chondroitin-sulphuric acid. 



1. Mucin Substances. 



Compared with the simple proteins the mucin substances are poorer 

 in nitrogen and as a rule also have considerably less carbon. The carbo- 

 hydrate complex, whose nature has been shown by the investigations 

 cf FR. MuLLER 3 and his pupils, occurs, so it seems, in the mucin sub- 

 stances as a polysaccharide related to chitosan, which on hydrolytic 

 cleavage yields glucosamine (chitosamine), and, at least in most cases, 

 acetic acid also. The mucin substances differ very markedly among 

 themselves, hence we divide them into two groups, the mucins and the 

 mucoids. 



The true mucins are characterized by the fact that their natural 



1 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. 



2 See Schulz and Ditthorn, Zeitschr. f. physiol. Chem., 29; A. v. Ekenstein and 

 Blanksma, Chem. Centralbl., 1907, 2. When both carbohydrate groups are simul- 

 taneously combined in one body, then probably we are not dealing with a chemical 

 individual, but rather with a mixture. 



3 See Fr. Miiller, Zeitschr. f. Biologic, 42, which contains all the pertinent litera- 

 ture, and also L. Langstein, Die Bildung von Kohlenhydraten aus Eiweiss, Ergebnisse 

 der Physiologic, Jahr. I, Abt. 1. 



